A quarter of a mile further on the slope changed and the district was thickly built up. The errand boy soon entered a store. Willie had just time for a quick glance at the sign on the window. It read, "Fritz Berger, Fancy Groceries." Then Willie opened the door and followed the errand boy into the place.

A florid, burly man with upturned mustaches stood behind the counter. The errand boy was talking to him. In his hand he held a silver dollar.

"Here is the money for Mr. Baum's sugar," he was saying.

"Good!" said the grocer, seizing the coin, which he dropped in his pocket. Then he turned to Willie. "Well?" he said inquiringly.

"Sugar," said Willie. "I want five pounds of sugar."

"I have no more," said the grocer. "It is all sold."

"Pshaw!" said Willie. "Where can I get some?"

"I don't know," said the grocer.

"Got any candy?" asked Willie.

"Sure. In that case."

Willie walked to the show-case and slowly examined the stock. "Give me ten cents' worth of those chocolates," he finally ordered.

The storekeeper weighed out the candy and dumped it in a bag. He took the proffered dime, dropped it in his till, and turned away.

Willie left the store and stood for a moment undecided as to which way to go. "Nothing doing there," he said to himself. Then he turned a corner and started down the hill. The supper hour was approaching. People were coming up the street from the ferry, homeward bound from Manhattan. A motor-car came chugging up the road and drew close to the curb. The driver turned his car about, clamped on the brake, and stepped out, leaving his engine running. Willie went on down the street and was soon in the midst of a throng coming up from the ferry. He stopped to look at a jeweler's clock, turned about, and started on his way to rejoin Roy. Suddenly he heard the softly whistled signal of the wireless patrol. He turned sharply about and saw Captain Hardy across the street. He dodged a motor-car that was rooming down the hill and crossed to his captain. There had been no sign of life about the little house since the grocer's boy came out.

"Come," said the leader. "I have seen the Chief and he is going to arrange it so that we can watch this place in comfort. We will go back home now."

They climbed cautiously to the road above. "By George!" exclaimed Captain Hardy suddenly. "You boys haven't had a bite to eat since breakfast. I forgot all about that."

"How about yourself?" asked Roy.

"Well, I haven't either, but that's different. I've had a chance to get something if I had thought of it. We won't wait until we get home to eat. There's a restaurant at the ferry-house. We'll have a good dinner there."

More than an hour passed before the three rose from their table. Another hour had gone by before they reached their headquarters. They were tired and sleepy. But their drowsiness vanished when Henry rushed into the living-room of their apartment and thrust a sheet of paper into Captain Hardy's hands.

"It's another message," he said, "and we deciphered it ourselves."

Captain Hardy stepped to the light and read the message aloud. "Five more transports sailed late this afternoon. All camouflaged."

"We know the man who sent that message," cried Willie. "We've been watching him all the afternoon, down on the hillside at Staten Island."

"But this message didn't come from Staten Island," said Henry. "The detector points straight east over Brooklyn, and the message was sent from a long way off. It was very faint."



CHAPTER VIII

WHERE MONEY TALKED

For a full minute the members of the wireless patrol stared at one another in speechless amazement. Then Willie broke the silence.

"I don't care where it came from," he said. "I just know that the man we were watching sent it."

"But how could he have sent it, when the wireless pointed to Brooklyn?" demanded Henry.

"Oh! I don't mean that he actually sent it with his own fingers," said Willie. "But we saw him watching the ships and there isn't any other place in the whole harbor where you can get such a good view of them. I just know he had something to do with that message."

"I'll bet the Germans have got a string of wireless outfits and that what he does is to stay in that house and spy on ships that pass through the Narrows and then telephone to one of these secret wireless stations," said the nimble-witted Roy. "And if that's the case he hasn't any wireless at all himself."

"If Roy is right," said Henry, "it's a pretty clever scheme. The secret service could take his house to pieces and not find a wire in it. Yet he's the man that's sending the messages, or at least starting them."

"Roy is doubtless correct," said their leader. "We know they have at least three stations and they may have many more. The object of that, of course, is to baffle any wireless man who may be on their track. If we hadn't stumbled on this spy post at Staten Island, we should have been completely blocked ourselves. But we've got something definite to work on now. We've got a definite clue. And sooner or later we will uncover some of their hidden stations. From now on we've got to watch this man on Staten Island as well as listen for messages. I don't see how we are to do it unless we send for more of the boys or move to Staten Island."

When the matter was laid before Chief Flynn he said no more boys were needed. Too many boys in one house would attract attention. So he arranged to transfer the wireless patrol to Staten Island. Living on the slope above the suspected house was a well-to-do but childless couple with a rather large house, who were warm friends of the Chief's; and they readily agreed, as a matter of service to their country, to take the wireless patrol into their home. So a wireless outfit was installed, with a concealed aerial, and the boys found themselves situated even more pleasantly than they had been before.

And it was well that they were pleasantly situated, for though their task was not difficult in one sense, in another it was extremely trying. Six hours a day each boy sat at the wireless listening in. Had it been possible to tune to longer wave lengths and pick up the interesting news with which the air was fairly alive, the task would have been anything but irksome. But to sit hour after hour with their instruments tuned to the short wave lengths used by the German agents and hear nothing, was trying enough. The watch on the spy's nest proved hardly less tedious. From a gable-window in the attic a very fair view could be had of the little house below. Here, on rainy days, a watcher sat during all the hours of daylight; and on other days the sheltering pines hid an observer. But day followed day, night succeeded night, and no message was registered on the wireless instrument nor did anything suspicious occur in the house under surveillance.

Indeed the fact that nothing did occur was in itself suspicious. For there was hardly a sign of life about the house. No man left it in the morning bound for business. No woman emerged from its door to go shopping of an afternoon. For days at a time nobody entered or left the place, excepting the grocer's boy who came with food.

Then one day a motor-car, with its top raised, chugged up the highway and climbed the steep driveway to the house on the cliff. Henry was in the attic gable on watch and he promptly notified his comrades. There was a rush for the third story, and four heads crowded close together as four pairs of eyes sought to identify the make and number of the car. But the name-plate was missing, and the license tag was so dusty that the number could not be read.

"Run down to the pines with this, quick," said Captain Hardy, thrusting his field-glasses into Willie's hand, "and get the number of that car. See if you can tell what make it is and look for distinguishing marks."

Willie scrambled down the slope through the concealing shrubbery and approached the house as near as he dared. But he had hardly reached his station when the driver ran down the steps of the house, sprang to the wheel, and was off at a fast pace. Willie climbed cautiously back to headquarters.

"Did you get its number?" asked his chief.

"No," replied Willie. "It was covered with dust. And I couldn't tell what make of car it was. But I saw the driver and I am sure I have seen him before and the car, too."

"That's not unlikely," said Captain Hardy, "if he lives anywhere near here. We've been here several days now."

"I'm sure I've seen that man somewhere," said Willie. "I wish I could remember where it was."

Another day passed and another, and still the little house on the cliff showed no signs of life. But one afternoon the monotonous watch came to a sudden end. Lew, in the attic gable, espied a fleet of transports coming down the bay. Instantly he spread the alarm.

"You boys slip down to the pines," said Captain Hardy to Willie and Roy. "If any one comes out of the house trail him. Now we'll find out whether this spy—if he be a spy—telephones his news or sends it out by messenger. The Chief has had the telephone wires tapped and is receiving a record of all conversations."

Lew continued his watch aloft. Henry sat tense at the wireless, waiting to catch any possible message, and Roy and Willie scrambled cautiously down to their favorite observation post in the pines. On came the transports, riding the waves in a stately column; yet the little house seemed as lifeless as ever.

"Watch close," whispered Willie. "Don't let anything escape us."

On came the ships, nearer and nearer, throwing the white spray away from their bows. They passed Robbin's Reef light. They drew close to the entrance to the Narrows. Breathlessly the boys awaited their nearer approach. The transports reached the narrowest part of the passage and still there was no sign of life in the little house. Willie gave a sigh of disappointment and started to speak; but before he could utter a word there was a movement in the window before them and the man they had previously seen appeared for a moment sweeping the Narrows with his glasses. Then he disappeared from sight.

"It's him!" exclaimed Willie, forgetting his grammar in his excitement. "Now he's either telephoning his message or getting it ready for a messenger. We'll soon know."

They had not long to wait. A figure was seen coming up the highway.

"It's only the grocer's boy," said Willie in disappointment. "This is the time he usually comes."

"I wonder if we aren't on a wild-goose chase," said Roy. "Maybe the man in that house isn't any spy at all. I begin to think so."

"I don't," maintained Willie. "I just know he's a spy, but how he sends his messages I can't figure out."

Just then the grocer's boy came out of the house. "There's no use trailing him," said Roy. "We already know who he is. While we're following him the messenger might come—if there is one."

"Captain Hardy said we should follow any one who left the house," said Willie, "so I suppose we'll have to watch this errand boy. You go this time, Roy."

In a minute Roy had reached the higher thoroughfare. He ran down the road at top speed and got to the grocery store before the loitering errand boy even came up into this higher road from the lower thoroughfare. But instead of entering the store, Roy turned the corner, retracing his steps in time to enter the store half a minute before the errand boy got there.

The grocer was behind the counter. "Have you any crackers?" asked Roy.

The grocer took down a package of Uneeda biscuits.

"You don't have any loose ones?" asked Roy.

"No, these are all we keep."

"Guess I'll have to take 'em," said Roy. "Got any candy?"

"In the case there," was the answer.

Roy walked over to the show-case and began to examine the stock. Just then the errand boy came in.

"Here's the money for the sugar," he said, handing the grocer a silver dollar.

The grocer took the coin and carelessly dropped it into his pocket.

Roy continued his inspection of the stock of sweetmeats. "Give me five cents' worth of gum-drops," he said.

The grocer began to weigh them out. A tall man with gauntlets and with motor goggles on his forehead came in.

"Hello, Fritz," he said jovially. "Got that sugar for me yet?"

"Just sold my last ounce," said the grocer. "I haven't been able to get a bit for three days."

"Himmel!" said the customer. "How much longer have I got to go without sugar in my coffee?"

He turned to go.

"Hello!" called the grocer. "Here's that dollar I owe you."

The man turned back, and the grocer pulled the coin from his pocket and dropped it into the man's gloved hand.

"Good luck to you," he said, then finished weighing out the gum-drops for Roy, and dropped the nickel in his cash drawer.

Slowly Roy retraced his steps. "Well, what happened?" asked Willie, as Roy rejoined him.

"Nothing," said Roy in disgust. "The errand boy came in and handed the grocer a dollar that he had collected for sugar. Pretty soon an automobile driver came in to get some sugar and the grocer said he hadn't any more, but he paid him a dollar he owed him."

Willie was silent, turning the matter over in his mind. "Then what?" he asked after a time.

"Nothing, except that I bought some candy and the grocer put the money in his cash drawer. Then I left."

"Where else would he put it?" asked Willie, abstractedly, as he tried to read some meaning into the grocer's apparently meaningless acts.

"Well," said Roy, "he didn't put the dollar the errand boy gave him into the drawer. He dropped that into his pocket."

"Why, that's exactly what happened when I was in there the other day," said Willie in surprise.

The daylight waned. Dusk came on. It grew too dark to see the spy's house from the pines. It was past time to relieve Henry at the wireless. The two scouts climbed to their own house for orders. As they came up the stairs they heard the voice of Henry.

"Come quick," he called. "I've got another message."

Everybody rushed to Henry's side. Captain Hardy seized the sheet of paper from Henry's hand, and counted the long string of letters written on it. Quickly he rearranged them in four equal lines. Then slowly he read the cipher. "Another transport fleet assembling. First five boats went to sea this afternoon."

"Where did this message come from?" he demanded, as he laid down the paper.

"From some point down the Jersey coast," said Henry, "and probably not more than twenty miles away."

A long silence followed. "We're simply up against it," said Lew dejectedly. "We don't get anywhere."

Suddenly Willie jumped to his feet with a cry. "I've got it! I've got it!" he almost shouted. "Why didn't I see it before?"

"Got what?" asked Roy, astonished.

Willie paid no attention to his question. "What sort of a looking man was that motorist?" he cried.

"A tall fellow, with black hair and with a big scar on his cheek," said the astonished Roy.

"I knew it," cried Willie. "I knew it! Now I know how the messages are carried. It's as plain as can be."

His fellows clustered about him. "What do you mean?" said Captain Hardy eagerly. "Explain."

"Well," said Willie, "when I followed that grocer's boy the other day, I saw him give the grocer a dollar which he said he had collected for sugar. The grocer put it in his pocket. But when I gave him money for candy he dropped it in his till. Just after I left the store and turned the corner a man drove up in a motor. I noticed him because he turned his car completely around and stopped at the curb. He got out and left his engine running. When I crossed the street to meet you, after you whistled, I dodged a motor-car. It was the same car, but I thought nothing of it." He paused, as though collecting his thoughts.

"Go on," said their leader eagerly.

"To-day," resumed Willie, "Roy followed that same grocer's boy from the house on the cliff to the grocery store and saw him give the grocer a dollar, which he said he had collected for sugar. The grocer dropped the coin in his pocket, but he put Roy's nickel in his drawer. A minute later an automobile driver came in. The grocer said he owed him a dollar and gave him the coin from his pocket. That driver was the same one I saw the other day."

"How do you know?" interrupted Captain Hardy. "You didn't see him to-day?"

"But Roy saw him. He's a tall man with black hair and with a scar on his left cheek. That's the man I saw, and it's the man who drove up to the house on the cliff the other day. I knew that I had seen him, but I couldn't remember just where." For a moment he stood silent, fairly panting with excitement.

"Well?" said Lew. "What about him? The grocer could owe him a dollar as well as anybody."

"But he didn't owe him a dollar," cried Willie. "Don't you see? The spy in the house below gave that dollar to the errand boy. He gave it to the grocer. He gave it to the motor driver. It's the same dollar. He didn't put it in the till with the other coins. He kept it in his pocket separate. That automobile driver is the man who carried the messages to the wireless. The messages are on the dollars."



CHAPTER IX

A FRESH START

Amazed, the members of the little patrol looked at one another silently.

"How could they send a message on a dollar?" demanded Lew at last. "They'd have to engrave it, and then they'd never dare to use the dollar again. Besides, it would be too dangerous. If the message were on paper, the paper could be burned or chewed up and swallowed, and the evidence of crime destroyed. But they couldn't erase the engraving on a dollar."

"I don't know how they do it," said Willie, "but I'm sure they write their messages on those dollars."

"Willie is doubtless right," said Captain Hardy. "We don't know how they do it, but the evidence leads directly to the conclusion Willie has come to. The spy in the house below us writes his messages on dollars and sends them through this grocer's boy and the motor-car driver to the various secret wireless plants the Germans evidently possess near New York. I think that is plain. And it indicates new lines of action for us. We must not only continue to listen in for messages and watch this spy's nest, but we shall have to follow this motor-car driver and also learn the secret of the dollars."

"Hurrah!" cried Roy, his eyes shining. "Now there'll be something doing." Then he struck a tragic attitude and declaimed, "Little do the treacherous hawks in yonder nest realize that the eagles of the law are about to swoop down on them."

"Some orator, Roy," said Lew. "If we're eagles, we must have wings. Are mine sprouting yet?" And he turned his back to Roy for the latter's examination.

When the laughter ceased, their leader went on, "You boys are to be congratulated for your discovery. You have accomplished a great deal. But what has been done is little compared with what remains to be done. And so far you have worked in safety. The work ahead may be very dangerous. The hidden wireless stations we are after are probably in lonely places. The men operating them are desperate fellows and will not hesitate even to commit murder. If one of you boys should follow this motor driver into a lonesome spot and then be caught, you might never return."

The smiles faded from the faces before him. But the grave looks that succeeded were not expressions of fear. Rather they were looks of determination—the same set marks of grim purpose that Captain Hardy had seen on these same youthful faces when the wireless patrol was stalking the desperate dynamiters at the Elk City reservoir.

Again it was Roy who brought back the smiles. "If we have to follow that automobile driver," he said, "it's a question of 'where do we go from here, boys?'"

"Only the boy who does the following can answer that question," answered Captain Hardy. "But there are several matters that we can decide at once. I think that we've determined pretty definitely that the man in the house below us——"

"In the hawk's nest," interrupted Roy.

"Well, the man in the hawk's nest," continued their leader, smiling, "is a German spy, that he is there to report the movements of our transports, and that he does it by means of messages sent out on silver dollars. Now we've got to get hold of one of those dollars. That might not be a difficult task in itself. We could hold up the grocer's boy and take the dollar away from him, or we might get it away from him by trickery and substitute another dollar for the stolen one. We might even be able to pick the grocer's pocket and give him a substitute coin. But neither plan would help us because the trick would soon be discovered and the spies would know that they are suspected. It wouldn't do us any good to get their code if they knew we had it. They would simply use another. What we must do is to locate their agents, one after another, learn their codes and ciphers, and catch their messages in the air. When we have laid bare the entire scheme and learned who their agents are, then the secret service can grab the entire organization at once and end this treachery for good."

Captain Hardy paused and looked uneasily across the room, as though lost in thought. His companions were quiet as mice, each also busy with his own thoughts.

"It's a long, hard task, boys," said the captain, after a time, and he drew a deep breath, "a long task and, from now on, a dangerous task. Whatever you do, boys, remember the Chief's warning. Above all else, we must be careful not to alarm the men we are watching."

As Captain Hardy rose to get his hat he said, "I don't quite see how we are to follow this motor-car driver without being detected. So I am going over to Manhattan to see the agent the Chief has put in charge of this investigation. Perhaps I'll have some interesting news for you when I return. Meantime, keep your eyes and ears open and be careful."

With renewed interest and determination the members of the wireless patrol returned to their posts. But though they listened faithfully at the wireless and uninterruptedly watched the hawk's nest on the cliff below them, no alarming sound came out of the air and no suggestive movement occurred within their vision.

Their captain came back with a smile of satisfaction on his face. But the members of the wireless patrol were too well disciplined to question their leader. They knew that, as always before, he would give them the proper orders at the proper time; and that if they obeyed those orders faithfully and intelligently, success would follow. But Captain Hardy was different in many respects from other commanders, and his subordinates were not at all like ordinary privates in an army. There was no question as to their loyalty, discretion, or intelligence; and their leader believed he could attain the greatest success by taking them into his confidence. So presently he answered the question that each boy was longing to ask.

From his pocket he produced detailed maps of all the neighboring country, so mounted on cheese-cloth, after being cut into squares, that they could be folded into small size without injuring the maps themselves. Thus the bearer could always follow his route, whether he walked or rode, whether the air was calm or the wind blew fiercely, by carrying in his hand the necessary map folded in small compass.

Now Captain Hardy spread out his maps full length on a table, and for half an hour the little group bent over them, heads close together, examining the topography of the city's environs as once they had studied the city itself. Marked to show altitudes, roads, byways, rivers, streams, marshes, woodlands, and even the buildings themselves, these maps enabled the little group of scouts to see, through their imaginations, every foot of the country about New York.

They visualized the great, flat, low-lying stretches of southern Long Island and New Jersey; the abrupt bluffs of Long Island's northern coast by the shore of the Sound; the various watery arms that encircle the American metropolis, permitting ships to sail in every direction; the majestic Hudson leading straight north through a wonderful country of rocks and hills, the impressive Palisades flanking its western bank with their towering perpendicular walls of stone; and the rocky, rolling country lying west of them, interspersed with streams and swamps and woodlands and open fields and clustered villages. And when they had finished their study of the maps, they knew more about the topography of the country they had studied, its roads and paths and groves and elevations and other physical characteristics, than half the people who lived in the region. So they were prepared, if need be, to find their way about with little difficulty. And it was well they were so prepared. In the dangerous days to come they were to need all this knowledge.

When they had studied the maps to their hearts' content—and each of the four boys again and again examined them—Captain Hardy folded the maps and thrust them into a waterproof cover. They made a neat little packet like a thin book.

"You will be interested to learn what the secret service has found out," said Captain Hardy, as he stowed the maps in his pocket. "When I left here, I reported immediately to the man in charge of this particular investigation. Our discovery seems to me so important that I ventured to ask why the secret service men didn't take the case up themselves, as they would no doubt get along much faster than we possibly can. For it seems to me message sending ought to be stopped at once. The agent said that all this was true, but that the secret service was so crowded with work it had to take up the most important matters first."

"Most important matters!" cried Roy, in indignation. "Doesn't the secret service consider the guarding of our troops important?"

"Yes, Roy. But whether the Germans know exactly when our ships leave or not, their submarines will be waiting for them and our destroyers will always be guarding the transports. But here in New York German spies are trying to create riots, to blow up buildings, to burn factories. They destroyed almost a million bushels of wheat in one fire recently. So you see that the secret service first must watch the enemies that are trying to destroy our greatest city. Our secret service isn't one-quarter as large as it should be. That is the fault of Congress. But meantime it is doing wonderful work, and it is a great privilege to be able to assist in that work."

"But what have they found out about this job?" demanded Roy.

"You're like a hound on a keen scent, Roy," said their leader. "Nothing ever takes you away from your objective. Well, this is what they've found. It seems that they have been keeping a record of the grocer's telephone messages, as well as those from the 'hawk's nest' down below. Every time transports sail, some one in Hoboken calls up this grocer and says, 'I have some sugar on the way. Do you want any?' And the grocer replies, 'Yes. How many barrels can you let me have?' And the man in Hoboken gives the number. That number corresponds with the number of transports about to sail. So you see how the grocer knows when to send his boy for the wireless messages. But before he sends him, he always telephones to the 'hawk's nest' and says, 'I have some sugar coming and can let you have five pounds to-day. Do you want it?' And the number of pounds he offers is the same as the number of ships that are to sail. So the spy below us knows what to look for. And I suppose the man in Hoboken also telephones the automobile driver when to come for the dollars."

"Who is this man in Hoboken that does the telephoning?" demanded Roy, when Captain Hardy had done speaking.

"Ah! That they don't know. He has always called up from a different place and has gotten away before the secret service could spot him. But the agent assures me that they'll have him soon. He always telephones from a station close to the piers where the transports load. The next time he calls for the grocer, the telephone operator is going to delay him while she notifies a secret service agent posted near by with a motor-cycle. So they'll spot him and trail him.

"And that reminds me," continued Captain Hardy, after a pause, "that we're to do a little motor-cycle work ourselves, and that Henry has been selected for the job because he is familiar with motor-cycles."

Henry's eyes lighted with pleasure. Not only was he the oldest boy in the wireless patrol, and Captain Hardy's first lieutenant, but he was one of those natural mechanics who seem to know instinctively how to handle tools and make things. Indeed he had constructed his own wireless outfit and shown his fellows how to make theirs; and he could repair a motor-cycle almost as skilfully as a garage man. So it was natural that he should be selected for this task.

But there was still another reason why his captain had chosen him for the work he had in mind. Though not so quick or clever as Roy, Henry was a keen observer and close reasoner. Moreover, he was entirely dependable, was very discreet, and being the largest boy in the party, was best fitted to take care of himself if he got into trouble.

"We are going to trail this automobile driver with a motor-cycle, as you have probably guessed," explained Captain Hardy to the little group of scouts. "And Henry is to do the trailing. Come, Henry. We'll go take a look at your machine. The secret service people said that it would be here in half an hour."

"Where? In this house?" asked Roy eagerly.

"No, not here, but at a house around the corner from the grocer's. It will always be in readiness for instant use."

As Henry put on his hat and followed his leader, the other scouts looked at him somewhat enviously. "Remember," said their leader, turning about, "each one of you has his work to do, just as Henry has. See that you do it."

At once the boys returned to their posts, while Henry and his captain passed out of the house and went down the street. Instead of going directly to their destination, the two made their way by a roundabout route and kept a sharp lookout lest they should meet the grocer or his boy. But they passed almost no one and came soon to a little white house, not far from the grocer's store, that was set back in a yard behind a high hedge. Connected with the house was a small garage, built so as to resemble an extension of the dwelling.

A keen-eyed woman answered their knock at the door and looked at them questioningly.

"We are the sugar refiners sent by the Federal Sugar Company," said Captain Hardy, repeating the words given him by the secret service agent.

"I've been looking for you," replied the woman. "Come in." And she led them at once through the house to the garage.

Henry was about to ask Captain Hardy what he meant by saying that they were sugar refiners, but when he saw the motor-cycle that awaited him he forgot his question and gave a sharp cry of exultation. It was a beautiful machine, with tires so strong and thick they were practically puncture proof and were evidently equal to any demand that was likely to be made upon them. Evidently the engine was one of great power. The frame of the machine was a dark gray; and Henry instantly noted the fact that there was an almost utter absence of nickel about the motorcycle. The spokes, handle-bars, and trimmings were all enameled black. The headlight was a powerful electric one, with a black cap over the lens. With great interest Henry examined the spark- and gasoline-controls, the motor itself, and finally the muffler, which was of the most improved variety. He looked in the gasoline-tank and found it full. The oil-tank was brimming. Every moving part had been carefully greased and cleaned.

"What's this?" cried Henry, of a sudden, noting what seemed to be an extra and unnecessary piece of framework.

"Take it out and see," said Captain Hardy, with a smile.

Carefully Henry examined the fastenings, to see how the extra tubing was adjusted. Then he drew it forth.

"A metal cane," he said, puzzled. "What is it? What is it for?"

Captain Hardy explained. Then he picked up a small electric torch, some well insulated wires that lay coiled on a near-by chair, and something that looked like a giant fountain pen. He handed these articles to Henry, and repeated what the secret service man had told him as to their use.

"Put them in your pocket and be very careful that you do not lose them," directed Captain Hardy. "Carry them with you so that you can run to your motor-cycle at a second's notice. Now replace that cane on the machine."

Henry slid the cane back and fastened it in place. It was gray, like the car, and seemed to be a part of it. Then Captain Hardy fastened the little map case above the gasoline-tank in such a way that Henry could pluck out a map as he rode.

"Now," he said, "there is nothing to do but wait until the automobile driver comes for another dollar. Then you must follow him wherever he goes. You must watch every movement he makes. But you must not let him see you. It's a hard thing to ask of you, Henry, for everything hinges upon your success."

A look of determination flashed in Henry's eyes. "I'll do my best," he said simply.

"I know you will," rejoined his leader. Then he added, with a smile, "Now we'll go back to the eagle's nest and wait for the hawk to appear."



CHAPTER X

THE PURSUIT IN THE DARK

Day followed day but that bird of prey did not appear. "A watched pot never boils," said Henry at last, trying to conquer his impatience; and he turned his mind from the task of following the automobile driver to the even more difficult task of securing one of the dollars. For sooner or later the wireless patrol would have to procure one of these mysterious coins. But Henry could see no way to accomplish that end without alarming the quarry. Day after day the little patrol discussed the question. It was useless to think of securing a coin from the man on the cliff, from the grocer's boy, or from the grocer himself; for none of the three had possession of the coins very long after they were marked. And what became of the coins after they left the grocer's hands could as yet be only guessed at.

Again and again, as the days passed, the members of the wireless patrol discussed the secret of the dollars, but nowhere could they find even the suggestion of a solution. Slowly time dragged on. Day followed day. The watch grew monotonous and tiresome. There were no signs of hostile activity in the hawk's nest and the secret service had no suspicious telephone conversations to report. It required all their resolution to keep the young scouts at their task of listening in. They even began to think that they had been detected and that the activities of the spy in the hawk's nest were ended.

Then, one afternoon, galvanizing them to sudden action, came a cryptic message from the secret service, announcing that the Federal Sugar Company could use experienced refiners at once. Henry took the message, and recalling what Captain Hardy had told the woman when they went to see the motor-cycle, at once guessed its meaning. He ran to Captain Hardy and repeated it.

"You guessed rightly," said Captain Hardy. "Hereafter we, too, have to use code messages, and we just carried out the spy idea about sugar. This message is to warn us that transports are sailing. Go to your stations, boys."

Lew flew back to the wireless. Roy and Willie hustled down to the pine grove. Henry, his heart beating fast, hurried away to his motorcycle station.

For a long, long time nothing happened. Then a line of transports came into view. Presently the spy appeared at his window, sweeping the channel with his powerful glasses. For several moments he studied the passing ships carefully, then withdrew from the window and was lost to sight. In a very few moments the scouts saw the grocer's boy, with his basket and a few small packages, enter the house, then hurry away. Roy trailed him directly to the grocery store, but did not enter.

Henry, meantime, impatient, like Paul Revere, "to mount and ride," stood peering out of a tiny window of the garage, awaiting the expected motor-car. In his eagerness minutes seemed like hours. As time passed and no motorcar came, he began to believe that none would come, that the spies had learned of the trap set for them, and that they had discontinued their work or devised some new plan of operation. So impatient did Henry become that he could hardly refrain from running into the street to see if any motor-cars were approaching. At last his anxiety was relieved. He heard the regular beating of a motor climbing the hill. Then as he glued his eye to the tiny window the familiar car, a powerful roadster, with its top raised, rolled by. Again Henry tried to catch the number and failed. Then he knew that the dust-covered license number was not dust covered by accident. Quickly he noted the treads of the tires, and the shape of the wheel hubs, axles, and springs, so that he could identify the car. Then it passed from his sight.

And now his anxiety suddenly grew a hundredfold. Always before, the car had returned the way it came. Suppose that this time it should go back by another route and he should miss it. He could not endure the thought. Quickly he opened the door and peered forth. The driver was just turning his car, as he had always done before. The matter was settled. He would pass Henry's hiding place on his return. Quickly Henry shut the door and waited with what patience he could command.

for what seemed like an hour he waited. His pulse beat fast with excitement. He could hardly compel himself to stand quietly by his window and wait. The old fear that the motorist had gone away by some other route returned and began to torture him. He wanted to run out into the street and assure himself that the car was still in sight. And then, when it seemed he could endure the suspense not a second longer, he heard the purring of a motor, and the car he was waiting for slid quietly by and began to descend the hill toward the ferry.

At once a new fear sprang up in Henry's heart. Suppose the motor-cycle wouldn't go. Suppose he should be so slow as to miss the ferry-boat. Desperately he flung open the door and trundled his motor-cycle out to the street. The roadster was only a block ahead of him. Speedily Henry pushed the cycle along the road. The motor began to bark and Henry leaped to the saddle. In another instant he was speeding after the roadster and was already so near it that he had to jam on his brake to avoid coming up to it. Near the ferry there was more traffic and Henry felt relieved. He dropped back a little distance and was almost completely hidden from the roadster by the carts and cars between them. So they proceeded to the ferry, the suspected driver bringing his roadster to a halt near the front of the ferry-boat just as Henry, following a string of wagons and carts, reached the other end of the craft. Then the whistle blew and the boat pulled out into the Bay.

But Henry had now no eyes for the sights in the harbor that had formerly so fascinated him. His entire attention was centred on the roadster. The driver of the roadster remained in his seat, calmly looking out over the Bay. Henry stood his machine against a post and sought a position near by where he was sheltered from the spy's observation by a huge coal truck, but where he could himself distinctly see the roadster by peering through the spokes of the truck wheels. Again he made a mental inventory of the distinguishing features of the car he was following. And before the ferry-boat reached Manhattan he could have passed a perfect examination as to the appearance of the roadster.

It was already dusk when the boat slid into its slip, and the heavy clouds overhead gave promise of a dark night. Henry was thankful. Up Broadway he followed the roadster at a safe distance, then up Park Row, and so to the Brooklyn Bridge. Across this magic structure, one hundred and fifty feet above the surface of the water, Henry continued to follow the roadster. The great buildings, piled skyward in huge masses, were twinkling with a million lights. Boats were coming and going on the stream below. Electric cars followed one another across the bridge in endless procession. Elevated railway trains thundered past unceasingly. Up-stream shone the fairy lights of the other bridges that span the East River. The Navy Yard lay in full view. But the scene that at other times Henry would have found entrancing, now he scarcely noticed. He had eyes for one thing only—the rolling motor-car ahead of him and the red eye that now glowed at its rear.

He turned on his light and at a safe distance followed the roadster, which was heading due east. They passed the business portions of Brooklyn. They left Prospect Park behind them. They traversed a region of apartment-houses. Then came less thickly settled districts, with block after block of private residences, each in its own little yard. And so they proceeded to the very outskirts of the city, where houses gave place to vacant lots and vacant lots were succeeded by open fields. Darkness had come. Traffic had grown less and less. Now there were no sheltering vehicles between himself and the roadster. A great fear of discovery sprang up in Henry's heart. He switched off his light, risking arrest, and rode on in the darkness. Occasionally he passed under a lone street lamp. And now he understood why his machine was enameled black instead of being nickel finished. It gave back no answering gleam when beams of light fell upon it. It was made for just the secret sort of work it was doing now. For, with his motor completely muffled, his lamp extinguished, Henry was now riding through the night like a dark shadow.

Long before this, Henry had slipped the proper map from its case and had followed his route as far as he was able to see. Though his eyes could no longer pierce the darkness, Henry knew that he was passing through a lonely, undeveloped section of land. Dimly he glimpsed tiny bits of woodland here and there. The lonely lights Henry occasionally saw were the lamps in isolated farmhouses. He could no longer tell exactly where he was, though he knew the road he was following. But he had watched his speedometer closely and he knew he was traveling about twenty miles an hour. He was keeping pace with the motor-car, but riding several hundred yards behind it. So they continued for a long time.

Suddenly the motor-car swung round a curve and vanished from sight. Henry knew the car had rounded a curve because he saw the lights swing. A minute later as he was about to reach the curve himself, he heard the rapid beating of hoofs and a team of horses came tearing round the bend and charged straight at him. Evidently the driver had lost control of them and it flashed into Henry's mind that they had been frightened by the roadster ahead. But he had no time to think of anything. The frantic animals bore down on him like an express-train. Quick as thought Henry turned sharply to the right and threw on his power. The horses were almost upon him. The driver glimpsed him, cursed him savagely for having no light, and gave a powerful heave on the reins. The horses swerved in one direction as Henry shot in the other, missing them by less than a foot. Before he could straighten his machine again, it had left the road and was plunging over the rough surface of a field.

Henry jammed his brake on so suddenly that it toppled him from the saddle, but neither he nor the machine was injured. He turned the motor-cycle about and headed for the road. And now his hair almost stood on end. In the darkness he could dimly see some great lumber piles, as large as houses. He had all but crashed into them at high speed. Now he understood why the roadster's light had disappeared when the car turned the curve. It had been hidden by these great lumber piles. Rapidly Henry ran back to the road. He knew the motor-car would now be far ahead of him. He should have to hasten to overtake it. He ran along the highway, pushing his machine, and leaped to the saddle when the engine began to explode regularly. Then he turned the curve and peered ahead into the darkness. The road seemed to lie straight before him, but the motor-car had utterly vanished.

For a moment Henry rode on, almost bewildered. Then he looked rapidly about him. No farmhouse was in sight to which the motorcar might have gone. No light gleamed anywhere. But he could dimly see trees here and there. And he made out a wooden fence lining the left side of the road.

"Lucky I didn't shoot in that direction when I met that team," muttered Henry. "I'd have gone clear through that fence." He dismounted, set his machine up, and took out his pocket torch. Holding it close to the road, he began to examine the highway. "There are the marks of his rear tires," he muttered.

And thankful indeed was the puzzled scout that he had learned so well at Camp Brady to observe carefully. He mounted his wheel and rode a few hundred yards further. Then he examined the road again. He found the tracks he was searching for. He rode on and dismounting, found in two places the telltale marks. But the third time he examined the highway there were no marks of the roadster's tires visible.

"He left the road between this point and the last stop," murmured Henry.

He went back a hundred feet and searched. There were no tire marks. Another hundred feet showed no prints in the dust. But the third hundred revealed the wheel marks. "Ah!" said Henry, "he turned off close by."

He set his wheel against the fence and went forward, following the prints with his light, which he shaded carefully and held close to the road. Within fifty feet the marks turned straight off to the left. The car had passed from the highway through a gap in the fence, into an open field. What the field was like Henry could only conjecture. He dared not flash his light around to see.

He ran back and got his machine, then followed the wheel prints into the field. They did not show readily on the grassy surface, and soon he had lost them altogether. At first a sense of fear clutched at his heart. He recalled his leader's words as to the dangerous nature of this duty. Here he was in exactly the lonely situation his captain had foreseen, by himself, and with no means of defense. The enemy he was trailing had disappeared. He might be a mile distant or he might be waiting for his pursuer, behind the nearest tree. Henry shivered with fear and stood irresolute. But the feeling passed when he realized that he had lost the trail, that his quarry had escaped him, that he had failed his captain. A wave of remorse swept over him. The sense of fear left him entirely, and he bent all his energies to the task of finding the motor-car. He hid his wheel in a thicket that he might work faster, pausing only to snatch from it the metal cane fastened to the frame.

Cautiously he glided forward, crouching as he moved, and taking advantage of every rock and bush he could see to screen himself. He held his breath and listened. Now he crept forward a foot at a time. Now he advanced swiftly for yards. He worked his way to the right and the left. But nowhere could he see what he was searching for, and no betraying sound came out of the thick blackness.

"It's no use," he said to himself bitterly, after he had searched for a quarter of an hour. "I have lost him, and if I am not careful I'll lose his message as well."

Near by he could dimly discern a tall stump. He ran over to it and on it laid his map, a pencil, his electric torch, his knife, the wires that he had been carrying in his pocket, and the giant fountain pen. Grasping the tip of his cane he gave a sharp tug and an inner lining slid outward. From this he drew out a third length, and from that a fourth. His metal cane was in reality an extension rod, not unlike a telescoping fishing-rod. It was fully ten feet long. In its curved handle was a small opening, like a keyhole. Into this Henry jammed the bayonet connection that terminated one of the wires. The other end of the wire he thrust into a like opening in the side of his big fountain pen. Into the opposite side of his pen he fastened one end of his second wire, attaching the other end of this wire to his knife, which he thrust deep into the earth. Then, raising the extended cane aloft with his left hand, he put the point of his fountain pen to his right ear and listened. The mysterious articles that the secret service had supplied constituted a complete wireless receiving set. He could catch any message sent from a point within six or eight miles.

He was not a moment too soon. Hardly had he gotten the fountain pen adjusted before there came a crackling in his ear. He rested his cane, upright, against the stump, and began to tune his instrument by sliding the cap of the fountain pen in and out. In a second he had tuned it perfectly. The sounds came to him with startling clearness.

"He's near at hand," muttered Henry.

He seized his pencil and wrote down on his map the letters that were sounding in his ear. Then with frantic haste he disconnected his instrument, telescoped his extension cane, and gathered up the different articles and thrust them into his pockets. As rapidly as he could pick his way, he went back to his hidden machine. He fastened the metal cane in place, and got everything ready for a quick start.

Suddenly a faint purring noise came to his ears. "Ah!" muttered Henry, "he's started his motor. He's off in that direction. What shall I do?"

His first impulse was to run at speed toward the purring motor, and to try to locate exactly the position of the hidden wireless station. But discretion showed him that was not wise. The spy might turn his lights on at any moment and Henry would be caught. Then everything was lost.

"I must make sure I can find the place in the daytime," muttered Henry. Carefully he gauged the sound, deciding whence it came. "He's right off there," he said. And with his heel he made a long mark in the turf, pointing straight toward the sound.

Almost before he finished, the sound grew louder and Henry knew the car was advancing. He shrank back into the thicket, dragging his motor-cycle with him. An instant later the roadster rolled softly past, not more than fifty feet distant. In a moment more the car had reached the fence and turned into the highway. Its lights suddenly flashed out and the car went bowling down the road toward Brooklyn.

Henry leaped from the thicket and ran toward the highway, pushing his motor-cycle before him. He paused at the opening in the fence, and with his knife smoothed a space on one of the posts and marked a cross on it with his pencil. Then he ran to the highway, started his motor, and was soon flying down the road in pursuit of the roadster. And as he had come, so he returned, with lights out, until Brooklyn was reached and the streets were once more alive with traffic.

At a safe distance he followed the unsuspecting motorist and saw him turn into a private yard in Flatbush. Instantly Henry dismounted, thrust his wheel behind a hedge that fenced a private residence, and gained a position where he could watch the spy's house. He saw the spy close and lock his garage and enter the house. Stealthily Henry approached and noted the house number. At the corner he got the name of the street. Then he hurried back to his hidden motor-cycle and was soon flying back to his comrades at the eagle's nest.



CHAPTER XI

AN UNSUCCESSFUL SEARCH

It was characteristic of Henry that he should tell the worst about himself first. In his own manly way he was willing to accept the blame for his failure.

"He got away from me," he began, so chagrined that he could hardly repress the tears. "I didn't find the hidden wireless and I have failed in my task."

Before his captain he stood with downcast eyes and tortured heart. His experience at Camp Brady had taught him that the wireless patrol expected every member to do his duty—and he had failed.

Captain Hardy looked at his lieutenant for a moment without answering. He had not the slightest idea of what had occurred, but he recognized instantly the manliness of Henry's report. The latter was offering no excuses, making no attempt to shield himself from the consequences of his failure.

"Suppose you tell us just what happened," said the leader gently, "and we can judge better how badly you have failed."

Gratefully Henry looked up. He had not expected a scolding. That was not Captain Hardy's way of disciplining his boys. But he had felt sure his leader would show how deeply he was disappointed, for Captain Hardy was terribly in earnest in this quest for spies. So once again Henry's heart went out to his captain. Rapidly he related what had befallen him. As he proceeded with his story, his leader's face lost its look of grave concern, his eyes began to flash with interest, his cheeks to burn with eagerness. When Henry's narrative had reached the point where the motor-car had disappeared in the field and Henry was searching for it. Captain Hardy held up his hand.

"Stop a moment," he interrupted. "You were in no wise to blame for what happened, and instead of being condemned for failure you are to be commended for your success. Many a boy would never have found where that car went. And even though you did not learn exactly where the car was, you have located the field and you may be sure that driver never went very far in a field. We shall find the place easily enough. Go on."

Henry looked at his leader gratefully and a happy light came into his eyes. "Do you really think I didn't fail?" he asked eagerly.

"Assuredly," insisted Captain Hardy. "I think that you have learned enough to enable us to locate this hidden station. Go on."

Henry proceeded with the story of his search in the dark, of his uncertainty as to what he should do, of his fear of missing the message as well as the car, and of how he had intercepted that message, marked the fence post, and located the home of the automobile driver.

"Why, Henry," cried Captain Hardy, when the recital was ended, "whatever put it into your head that you had failed? You have done well—exceedingly well."

"But I didn't find the hidden station, and you said that was so important."

"That is a mere detail, Henry. We shall find it easily enough. We have our experience at Elk City to direct us."

"That's just why I felt so bad," said Henry. "If these Germans have concealed their wireless plant as skilfully as the dynamiters did at Elk City, we may never find where it is."

"We'll try before we give up hope," said the captain smiling. "And even if we never find it, we now know something more important than the location of one of their several wireless plants. We know where another member of the gang lives. That is excellent, Henry, excellent! The Chief will be more than pleased. I know he is a great deal more concerned about this wireless situation than he permits us to think. The public is clamoring for protection for the troops and the Chief simply cannot accomplish one-fourth of what is demanded of him. If we uncover this gang for him, we shall do a very real service to America, boys."

"We'll do it," cried Willie vehemently. "We'll do it. We'll get 'em just as sure as we got the dynamiters."

"I believe we shall," smiled the captain. "And if that's the way you all feel about it, I know we shall. We're closing in on them fast. To-morrow we'll go out to that field Henry has marked and see what we can find in the daylight."

So it happened that the succeeding forenoon found the five members of the wireless patrol rolling rapidly toward the point of investigation, in a motor-car furnished by the secret service and driven by one of its agents. Henry sat beside the driver and pointed out the way, while the others crowded into the rear of the car.

With his map on his knees Henry traced the way. Speedily they passed through the built-up portion of Brooklyn and came shortly to the sparsely settled district through which their road ran. Henry scanned the way with curious interest. He had been over the road but he knew nothing of what he had passed. Occasionally they whirled by a tree close to the road that Henry thought he had glimpsed in the darkness. So they flew forward until Henry, looking eagerly ahead, cried out, "There are the lumber piles."

The driver slowed his car almost to a walk and they looked in the dust for telltale marks. Few teams had passed since Henry's adventure, and in the dust could still plainly be seen the marks of Henry's wheel as he had turned sharply into the field, and the narrow tracks of the vehicle that had almost run him down.

But Henry was more interested in marks of another sort. "There!" he cried suddenly. "See those tracks? They're the marks of the spy's roadster." And he pointed to parallel tread marks, one made by a chain tread tire and one by a diamond tread.

They passed on. Not many hundred yards distant was an opening in the fence. "That's the place he turned off," insisted Henry. "See that light place where I shaved the post?"

But they did not turn into the field. Instead the motor-car continued steadily on its way. A half mile up the highway was a road-house known to the driver.

"It's about eleven o'clock now," said the secret service man. "We'll have luncheon at the roadhouse and in the meantime we can stroll around and hunt up this wireless plant. We'd attract too much attention if we drove directly into the field."

They stopped at the road-house, ordered luncheon, and said they would stroll about until noon. Then they wandered, apparently aimlessly, about the place and into the fields. The country was nearly level, with slight depressions here and little hillocks there, and bits of woodland all about. The road-house was the only structure in sight, and when they had passed beyond a slight elevation, even this was hidden. Apparently there was not a soul in the neighborhood. They paused just inside a little grove and made sure that no one was following them from the road-house. Then they pushed rapidly on into the little thicket which Henry recognized as his hiding-place of the previous night.

After a moment's search, Henry found the mark he had made in the turf. "The motor-car was in that direction," he explained, pointing along his turf mark.

His fellows looked in the direction of his outstretched arm. At a distance of a quarter of a mile was a thick little grove. Henry was pointing straight at the heart of it.

The scouts had kept themselves well hidden in the thicket as Henry was finding his mark. If any one was in the wood, that person could not as yet see them.

"I have no doubt we shall find the secret station in that grove," said Captain Hardy. "I see several tall trees sticking up above the others that might conceal aerials. I doubt if any one is there now, but some one might be. So we shall have to approach carefully and in such a way that we can capture any one who might be within the grove. Suppose we advance on it from all four sides, as we did on the willow copse at the Elk City reservoir. Then if any one is within the grove we shall see him."

The leader gave each boy his orders and the advance began. Henry was to circle and enter the woods from the rear. Roy was to approach from one side and Willie from the other. Lew was to go in at the front. Captain Hardy and the secret service man were to station themselves outside the wood so that they could see every point of its exterior and detect any one leaving it. Each glided away toward his post.

At a given signal from Captain Hardy, the boys began to work their way silently from their posts into the grove. This was small in extent and such precautions seemed almost unnecessary. But after their desperate experience with the dynamiters, the members of the wireless patrol were taking no chances. They knew full well that discretion is the better part of valor. And they knew, in addition, that the success of their search might depend upon the caution with which they proceeded. So they went forward, when the captain's signal rang out, like so many Indians on the war-path, stalking a hated enemy.

Indeed they were almost as invisible as Indians. Each had circled skilfully to his post. And now each crept forward silently, slipping from rock to bush, taking advantage of the slightest cover, and advancing so stealthily through the tall grass that even the two men on watch outside the grove could hardly tell where the scouts were moving. And any one inside the grove could not have detected them at all.

The four scouts reached the four sides of the grove almost simultaneously. Each of the four crept round the trunk of a big tree and squatted down with the trunk at his back, to look and to listen. From side to side their eyes roved, examining every tree and stump in sight. But they saw nothing on the ground or in the branches overhead to alarm them. There was no indication of human presence other than their own; and Willie was certain that the wood was deserted, for several small flocks of birds flew up in alarm as he penetrated the grove. Had other men been within the wood, he knew the birds would long ago have been frightened away.

Slowly the four scouts worked their way toward the centre of the grove, gliding round the trunks of trees and stopping every few feet to look and listen. But they heard nothing, saw nothing, to indicate that any man was within the grove. Each one, as he advanced, scouted to right and left of his line of march, so that when the four met in the centre of the wood, they had covered every rod of ground within the grove. And they had found nobody.

What was more, they had seen no signs of a wireless outfit. But, in view of their experience in searching for the dynamiters' hidden wireless, this was not surprising. None of the scouts had expected to find the secret plant without a thorough search. As soon as Captain Hardy and the secret service man joined them, a systematic search of the wood was begun.

There could not have been more than two hundred trees in the little grove. Satisfied that the place contained no enemy agents, Captain Hardy took his company to one end of the ground and began a careful examination of each tree. The six searchers strung out in a line across the grove, testing each tree as they advanced. They scanned the trunks and thumped them with clubs to make sure that they were not hollow. They peered at them from all sides, looking for holes and hollow limbs. With sticks they scratched away the leaves from about the bases of the trees, turning up the soil for several inches and testing it for hidden wires. All the trees seemed sound. No hollow limbs were discovered. No suspicious marks were found in the earth about the tree trunks. The tall trees noted by Captain Hardy seemed never to have been touched by man. From tree to tree the search proceeded until every tree in the grove had been tested and the scouts were on the far edge of the wood. But no hidden wire, no secret instruments, no skilfully concealed aerials were found.

Blankly the searchers looked at one another. "It must be here," said Henry. "I am absolutely certain that the motor-car came from this direction and was about this distance from where I stood. And the signals were so loud and clear that I'm just sure they were sent from some spot close by."

"Let us look for wheel tracks," suggested Captain Hardy. "If we can find where the car stopped, we shall know that the message was sent from some point near by. Search along the sides of the grove first."

The party divided, and three searchers examined the ground along each side of the grove. Walking abreast and several feet distant from one another, they covered a broad strip of ground. Twice each party retraced its tracks but found nothing.

"Try another strip, farther away from the grove," said Captain Hardy.

Again the searchers lined up and went slowly forward on either side of the woods. Bending low, stepping slowly, sometimes kneeling to examine a suspicious mark, they moved carefully on. The thick turf had taken no telltale imprint.

"I fear it's useless," sighed the leader.

"Let's try again," pleaded Willie. "The car was here. We know that. And somewhere it was bound to make a mark. It might have gone beyond the grove."

They made another search, this time extending their examination to the land beyond the wood. Suddenly Roy gave a cry. "Here it is," he called.

The others ran to him. And there, sure enough, in a little bare spot between two hummocks of grass, was the plain imprint of a diamond tread. Instantly Roy and Willie dropped to their knees and began to feel along the line of the tire mark.

Henry and Lew, meantime, searched to right and left of them. "Here's his other wheel track," suddenly cried Lew, and there, sure enough, was a distinct impression of a chain tread tire.

They proceeded in the direction in which the car had been moving. "Here's where he turned," cried Henry.

The turf before him was torn and ragged. Distinctly they could see the impression made by the driving wheels as they gripped the ground in starting.

"Then here is where he stood," said Captain Hardy. "It is immediately behind the wood. Your mark pointed straight enough, Henry, but your man was farther away than you thought. Probably he ran behind this grove to make doubly sure he would not be seen from the highway. The hidden station must be in this end of the grove. We'll search again."

Once more they plunged into the wood. Again they examined every tree. Up one trunk after another shinned Roy and Lew, who were born climbers. But hunt as they would, search as they might, they found nothing to indicate a secret wireless. At last, completely baffled, they gave up the search.

"It's here," insisted Captain Hardy. "Our experience at the Elk City reservoir makes me sure of that. They're too clever for us. But we'll get them yet. We'll follow that roadster so closely next time that we can't miss the secret. It's too bad, boys, but don't be discouraged. We have done much to come so close. Now we'll go back to the road-house. It's long past time for luncheon."



CHAPTER XII

ANOTHER OBSTACLE

Time wore on. Now that there was something definite to work on, the secret service began to take a more active part in the spy hunt.

"You have helped us greatly," said the Chief to Captain Hardy, one day. "My men were so rushed with work that they simply could not take the time to go hunting round for clues. But now that the wireless patrol has furnished those clues, we shall be able to follow them up. But we want you to continue at work just the same. You can still help us."

But the members of the wireless patrol, and especially Henry, found small satisfaction in the Chief's praise. They had not come to New York merely to furnish the secret service with clues. They had come to uncover the system by which spies were betraying the movements of our transports. At the Elk City reservoir they had succeeded where trained men had failed; and they meant to succeed here also. They felt that the Chief was patting them on the head, as it were, and telling them that they were good little boys. They meant to show him they were the equals of his own men, even if the Chief's words, instead of pleasing them, stimulated them to half angry activity.

"He needn't think that just because we're boys and come from the country we aren't any good," argued Roy. "That's the way everybody talks about boys. That's the way they talked about us at Elk City until we caught the dynamiters and showed them what we could do. We'll show Uncle Sam's men, too. I don't care if they are famous detectives. We'll get these fellows ourselves. We're not going to have the secret service step in now and take all the credit."

But it was one thing to talk so confidently and quite another to accomplish the end they were striving for. They had not yet discovered a single one of the hidden wireless stations, and the secret of the dollar was still a secret. As far as the members of the wireless patrol could see, it was likely to remain a secret. How they could secure one of the dollars without being detected, they did not know; and how they were to read the message, even if they did get the dollar, was more than they could see; for by this time they had dropped the idea that the messages were engraved on the coins. More and more those dollars appeared a great and insuperable obstacle.

"Couldn't we manage to see the spy when he marks those dollars?" asked Roy. "Is there any way that we could get into his house and hide, so as to watch him?"

"You mustn't think of trying," said Captain Hardy decisively. "But possibly you could find a new place to watch from that would enable you to see him better. These field-glasses of mine are very powerful, and if you can find the proper view-point, you can see him well, even from a distance."

Without a word Roy grabbed his hat and darted out of the house. A second later he was slipping through the thicket on the sloping hillside. Cautiously he crawled from one point to another. The only station that gave any promise of success was the pine grove originally selected. The tree from which they had been watching the spy's house was a giant pine that towered above every other tree in the grove. But the scouts had never dared to ascend beyond the protecting foliage of the other trees, lest they be detected. So they had been looking upward at an angle, as they watched the spy's house. Roy now saw that if he were to climb high up in the big pine, he would be on a level with the spy's windows, and could doubtless see clearly into the house. The difficulty would be to make the climb without being detected.

Roy made his way back to headquarters and reported on his observations. "I didn't go up," he said, "for fear he would see me."

"You were wise," replied Captain Hardy. "We must devise some plan by which you can get up the tree unnoticed."

"Camouflage!" said Willie suddenly. "Fix one of us up like a pine tree. Then he won't see us."

"Just the idea," said Lew laughing.

"We'll have to use the smallest boy in the bunch," said Captain Hardy, "and that's you, Willie. Come. We'll see what we can do with you. Go get me some samples of pine bark and needles."

Willie speedily got the desired objects. Captain Hardy examined them critically. "You ought to have a dark brown suit, painted with irregular stripes, like branches, and dabs of green, like foliage."

"Don't forget his face," cried Roy in glee. "That will have to be painted brown and green also."

A laugh went up. "I'm merely telling what ought to be done, Willie," said Captain Hardy reassuringly, "not what we shall do. We have to guard against observation by persons other than this spy. If the neighbors saw a boy going out of here garbed the way you want Willie fixed up, Roy, they would begin to ask questions. And we don't know what the spy's relations are with his neighbors. What we shall have to do is to dress Willie in clothes as nearly the color of the tree as possible. We can get shoes, stockings, and a suit of clothes to match the tree trunk. We can get a cap the shade of these pine-needles. That leaves hands and face. They, too, must be disguised. A pair of gloves of the proper shade will take care of the hands. But what about the face?"

"Nothing for it but to paint it," said Roy, his eyes dancing.

"I guess you're right," said Captain Hardy. Willie made a wry face. The captain saw him. "The trench raiders blacken both their hands and faces when they steal out into No Man's Land at night," he said. "But we won't use real paint, Willie. We'll get some theatrical paint that comes off easily. I'll get the necessary materials at once."

He noted down the sizes needed and went out. And it was well he acted so promptly. That very afternoon a message from the secret service informed them that more transports were sailing.

"Come with me and get on your pine tree outfit, Willie," suggested their leader. "You other boys go to your stations at once."

Henry's task henceforth was to trail the driver of the roadster. He hurried away to his waiting motor-cycle. Lew was at the wireless key again. Roy scurried out to the pine grove, and Willie followed his captain to be "camouflaged." A few moments later, dressed in his new brown clothes, and a chocolate brown in complexion, he slipped from the house and joined Roy.

Impatiently they waited for the first transport to appear. It was a long time coming. But finally Willie picked it out with his glasses, far up the Bay, as it nosed its way steadily through the rolling waves. Behind it was another transport. As the ships drew near, Willie mounted as far up in the tree as he dared, crouching behind the tops of the surrounding trees, and hugging his own tree trunk, motionless, awaiting his opportunity to climb to his ultimate post. His heart beat fast. His legs shook slightly with excitement. He was trembling all over, so eager was he to make the ascent. On came the boats. Long ago they had passed Robbin's Reef. Now they were well into the Narrows. Suddenly the spy appeared at his window, sweeping the channel with his glasses, his hands shutting off his vision on the sides, like blinders on a horse. Quickly Willie scurried up the tree, wrapping himself closely about the slender trunk, concealing as much of his body as he could, and snuggling behind the sparse clumps of foliage. Then he brought his glasses to bear, and sat silently studying the spy's house.

The interior of the dwelling was as he had guessed it to be. There was no partition wall in the forward part of the building, a single column upholding the ceiling, so that, above the low sash curtains, Willie could see entirely through the glassed-in room. This was more than comfortable. Willie saw a row of low book-shelves lining the north side of the great room. There were numerous fine pictures and plaster casts here and there. A piano stood in one corner, a talking-machine in another. The light within seemed to flicker, and Willie guessed that in the rear of the room, where he could not see it, a log was burning in an open fireplace; for the days were growing very chilly.

But before Willie could complete his observations, the spy turned from the window and walked toward a large, flat desk in the centre of the room. Willie shrank close against the tree and remained as motionless as a stone image. But the spy never once glanced out of the window. He sank into a chair before the desk, switched on an electric desk light, and began to write on a piece of paper. Evidently he was arranging his message. When this was done to his satisfaction, he reached into the desk and drew forth a dollar. Willie could see it plainly as the spy laid it on his desk blotter, under the lamp. Intently Willie strained forward. The spy leaned forward and fumbled about the bottom of his desk. His hands and arms were hidden and Willie could only conjecture what was happening. Then Willie gave a little gasp of surprise as the spy straightened up and laid on the blotter beside the dollar a curious little thing like nothing Willie had ever seen. Evidently it was of metal for it shone under the light. Willie screwed up his face as he strained his eyes to identify the object. It seemed to be a disc of exactly the same size as the dollar. Yet it was not solid, because Willie could see the blotter through it. To Willie the thing resembled nothing so much as a spider-web. What it was, Willie could not even guess.

Meantime the spy had pulled open a drawer, from which he took a slender instrument, which also Willie could not identify. But evidently it had a sharp point; for the spy, after placing the disc on the dollar, scratched the milled edge of the coin with the little instrument, then he began to make marks here and there through the little disc, on the surface of the dollar. From time to time he turned the coin, and occasionally he looked at the writing on his paper. He seemed quite expert, for he worked fast. He finished his task and leaned over behind his desk, evidently to put the curious disc in its secret repository.

Quick as a flash, Willie slid from his exposed perch and safely gained the concealing shelter of the lower tree tops before the spy straightened up again. Willie climbed on down the tree and joined Roy at the usual observation post.

"What did you see?" asked Roy eagerly.

When Willie had told him, Roy groaned. "Gee! That makes it all the harder. Now we've got to get one of those discs as well as a marked dollar before we can discover how they send their messages."

The grocer's boy came and went. Roy trailed him back to the store, but prudently kept out of sight. There was nothing to be gained by entering the store again. Meantime Willie scrambled up to the house and related to Lew and his captain what he had seen. And they agreed with Roy that the problem, instead of being easier, had become more difficult.



CHAPTER XIII

WHAT HENRY DISCOVERED

Henry, meantime, was waiting at his station with eagerness and quickened determination. Despite his leader's generous words, Henry felt in his heart that his last effort had been a failure. It was true that he had made it possible to learn the identity of the driver of the roadster, and that the secret service men had in the meanwhile been looking up the man's record; but Henry felt that he should also have discovered the location of the secret wireless. Now he made up his mind that nothing should balk him in the present attempt. That neither accident nor anything else should hinder him from accomplishing his purpose. He would be more skilful than he had ever been before. He would watch closer. He would follow his quarry, as silently as a shadow and as closely. He would do all that his leader expected of him—and more.

Thus resolving, steeling his mind to the greatest effort of his life, Henry stood at the little window in the garage, all atremble with eagerness. He thought he knew every inch of the spy's roadster, but when that car finally rolled past, Henry studied it as he had never studied anything before. Again he noted the tread of each tire and looked for cuts or other distinguishing marks in them. As good luck would have it, a turning wagon obstructed the roadster just as it reached the little garage, and the roadster came almost to a dead stop. Henry studied its running-gear, its radiator and bonnet, its dash-board and wind-shield. And when his eyes got so far, they went no further. The standards that held up the wind-shield were bulkier and thicker than any other such parts Henry could remember. The difference was not great, yet there was a difference; and like the accomplished scout he was, Henry noted that difference and questioned it. But, like Willie with the spider-web disc, he was completely puzzled. The enlarged standards might mean anything or nothing. The car rolled on and again Henry looked in vain at the number. Some part of it was always dust covered. But Henry observed that the hidden figures were not the same from day to day.

When the car returned from the grocer's, Henry jumped to his motor-cycle and made his way to the ferry by a route different from the roadster's. He knew he was taking a chance, but he also knew that an accomplice might be trailing the roadster to see if the latter were watched. Henry could follow the spy to the ferry once without arousing much suspicion; but if he were twice seen to do so, his usefulness might be ended. He knew when the ferry-boat would leave its slip and he made his way aboard just before the gate closed.

At once he had a feeling that he had acted wisely. The roadster was again in the forward part of the boat, but this time the driver did not sit placidly looking out over the Bay. He seemed nervous, and every little while turned sharp around and looked about him. Fortunately Henry had concealed his wheel behind a truck and was himself where the spy could not see him. When he noted the spy's restlessness, it flashed into his mind that perhaps the secret service men who had been investigating this spy had not been so careful as they should have been, and that the spy had taken alarm. It was a discouraging thought, for it made Henry's task vastly more difficult. Wisely, therefore, he went into the cabin and sat down. The spy could not see him, and if the latter should stroll about the boat, there was nothing to indicate to whom the motor-cycle belonged.

As the gate opened and the roadster rolled from the ferry-boat, Henry prudently remained well behind it. Up Broadway they went, as fast as the traffic would allow, their pace gradually quickening as they drew away from the congested lower end of the island. The spy drove straight up Broadway. He circled Union Square and continued north. He passed Madison Square and still held to Broadway. Past the shopping district, past Longacre Square, past Columbus Circle, the roadster continued, still on the city's main highway. And at a discreet distance Henry followed.

Now they reached the apartment-house district and slid past block after block of bulky living apartments. And so they continued past Columbia University and down the grade beyond. And here Henry's troubles began. The roadster turned to the left, and Henry knew the driver was making for the Fort Lee ferry.

How should he gain the boat unnoticed? How should he follow, undetected, along the Jersey roads? For after they had crossed the Hudson there would be an end to that concealing traffic that had so far hidden him. He must follow the roadster over lonely roads and yet remain unseen. It was a problem to disturb any one. And it worried Henry not a little. Fortunately dusk was at hand, though the curtaining darkness would not fall for some time.

When the boat reached the Jersey shore, Henry permitted the roadster to get a long start before he went ashore. The spy turned to the right and began to climb the long grade parallel to the river, that would lead him to the top of the Palisades. When the roadster was almost out of sight, Henry mounted his motor-cycle and followed. Even if his quarry should pass completely from view, Henry had no fear of losing him; for the roadster's tracks were plain in the dusty road.

The dusk deepened. As it grew darker, Henry came closer to his quarry, though he kept behind elevations and curves in the road so as still to remain invisible to the driver of the car ahead. Thus they rode for some miles. The country was as Henry had pictured it from his study of the maps. It was sparsely built up, woodlands were on every hand, and the surface of the land was rolling and rock-strewn. It was an excellent place in which to hide—and also an excellent place in which to dodge one's enemies. As Henry thought of this, he drew closer and closer to the car, though still seeking to remain out of sight. As the light failed, and it became difficult to distinguish the marks in the dust before him, Henry drew up so that he could see the roadster, but he discreetly rode close to the side of the highway, where the overhanging trees shadowed him. Even had the roadster's driver been looking straight in his direction, he might never have seen Henry. He was, as he had determined to be, a veritable shadow.

So they rolled northward. At last it grew dark. The driver of the roadster switched on his lights. Now Henry crept still closer. He was in the dark, his lamp unlighted, his motor running silently, and he had no further fear of discovery.

It was well that darkness had come. They had now reached a lonely region where there were few houses. Here, Henry judged, was an excellent place for a secret wireless. And he judged correctly, for hardly had the thought come into his mind before the roadster turned sharply to the left and disappeared. Henry darted up the road. He came at once to what he judged was a large field. Trees no longer bordered the highway on the left side. Dimly Henry saw objects here and there which he thought were boulders and clumps of bushes. He saw no light and stood for a second peering into the darkness, listening with bated breath. Straight ahead of him he heard the faint purring of a muffled motor. He knew that he was not many hundred feet behind it and that this time the car could not escape him. He thrust his motor-cycle into some near-by bushes, first whipping out his metal cane. Then he ran speedily but carefully after the car.

Evidently it was moving cautiously. Henry rapidly drew near to it. When he had come so close that he could see it distinctly, he dropped to a walk and began to look about, trying to see what was around him. Here in the field it was lighter than it had been on the highway under the shadowing trees. The field was, as Henry had guessed, a piece of wild land, grown up with thickets, with great boulders here and there. Directly ahead of him was a clump of bushes. Henry hastened to put them between himself and the car. It was well he did; for hardly had he gotten behind them before the car stopped and the driver got out. The car was not more than two hundred feet distant.

Henry dropped to the ground and lay still for a moment. Then he crept, like an Indian, toward the sheltering thicket. Through it he advanced until he was not more than fifty feet from the motor-car. He could see with fair distinctness, but was himself completely concealed. He lay like a log, watching intently.

The driver unfastened his top and slid it backward. As he did so, his overcoat caught on the open door and he gave an exclamation of impatience. When he had laid his top back, he lowered the upper half of his wind-shield. Then, standing on the running-board, he tugged at the top of his wind-shield standard. Up came a sliding inner tube. In a flash the entire mystery stood revealed to Henry. The wind-shield standard contained a collapsible mast, like the telescoping cane he held in his hand. Doubtless an aerial was now fastened to the mast. Somewhere within the car was a wireless outfit. Instead of having many secret stations, the Germans had this one portable station.



"How clever!" thought Henry. "And how well they deceived us."

The spy proceeded to run up his mast. It must have reached twenty feet into the air. And the aerial was dangling from it, too. Evidently the spy had fastened that on before raising the mast. Fifty feet distant stood a tree. The spy took something from the baggage container and walked over to the tree, where, Henry judged by the sound, he was fastening a hook. Then the spy carried over the other end of his aerial and fastened it to the hook. In the darkness Henry could see nothing of the details of this outfit, but he realized that the spy now had an aerial at least fifty feet long and well above the ground. For short distance communication it would answer perfectly.

The spy returned to his car and got into the seat beside the driver's. Henry wormed his way forward as far as he dared, hardly breathing, fascinated by what he beheld. For now he could see plainly. The spy had turned on a tiny light on his dashboard. Cautiously Henry rose to his feet, keeping behind a thick bush, and peered over the side of the car. The spy took a key from his pocket and unfastened a hidden lock. The entire cowl board turned down, revealing a compact but powerful wireless outfit. The aerial wire evidently was strung up within the collapsing mast.

From within the cowl the spy drew forth a curious metal disc, not unlike a spider-web, and like nothing Henry had ever seen. He did not know what it was. He hardly breathed as he stood watching. Then the spy took a dollar from his pocket, examined the milled edge until he found a scratch, fitted the curious disc over the dollar, and turning the coin in his hand, slowly began to make letters on a slip of paper on the inverted dash. When he had finished writing, he fastened the disc back in the cowl, dropped the dollar in his overcoat pocket, and began to send the message he had deciphered from the dollar.

Henry leaned forward. He had no need of his own receiving instrument to catch the letters. And he could not have used it if he had needed it. But it was not important that he should catch the message. The powerful sparks that were leaping across the spy's spark-gap told him that a battery of considerable force was being used, and he knew that Lew would catch that message away back on Staten Island. Lew had caught the preceding message from Long Island, and it had been sent from a distance fully as great as this. With distinctness the letters came to Henry's ears and he realized that the man before him was an expert operator. But the letters he heard made no sense. They would have to be deciphered before the message could be understood.

However, it was not the message that Henry was thinking of. It was the dollar in the man's overcoat. "How could he get it? How could he get it?" he asked himself over and over. A hundred wild ideas flashed through his head, but he could think of no way to secure the coin without betraying himself.

Even as he was considering the matter, the spy finished sending his message and snapped off his light. Tiny as the illumination had been, the man was apparently completely blinded by the sudden darkness. As he stepped from his seat, his overcoat again caught on the swinging door. With an impatient oath he tore the coat from him and flung it on the running-board. Then he felt for his tools and walked over to the tree to lower the far end of his aerial.

Henry's chance had come. With a bound he was beside the car. Crouching, he seized the huddled coat, ran his hands tremblingly over it, located the pocket, found the dollar, dropped the coat where he had gotten it, and slipped back to his cover.