Tom Swift had decided on another flight for his new craft before he would let the government experts see it.

"Silent Sam must do his very best work for Uncle Sam before I turn him over," said the young inventor.

"And after this flight I'll offer the machine to the government, and then devote all my time to finding Mr. Nestor," said Tom. "I'd do it now, but private matters, however deeply they affect us, must be put aside to help win the war. But this will end my inventive work until after Mr. Nestor is found—if he's alive."

Preparations for the test flight went on apace, and one afternoon Tom and Jackson took their places in the big, new aeroplane. He no longer feared daylight crowds in case of an accident. They made a good start, and the motor was so quiet that as Tom passed over his own plant the men working in the yard, who did not know of the flight, did not look up to see what was going on. They could not hear the engine.

"I think we've got everything just as we want it, Jackson," said Tom, much pleased.

"I believe you," answered the mechanician. "It couldn't be better. Now if—"

And at that moment there came a loud explosion, and Silent Sam began drifting rapidly toward the earth, as falls a bird with a broken wing.



CHAPTER XX

QUEER MARKS

"What happened?" cried Jackson to Tom, as he leaned forward in his seat which was in the rear of the young inventor's.

"Don't know, exactly," was the answer, as Tom quickly shifted the rudders to correct the slanting fall of his craft. "Sounded as though there was a tremendous back-fire, or else the muffler blew up. The engine is dead."

"Can you take her down safely?"

"Oh, yes, I guess so. She's a bit out of control, but the stabilizer will keep her on a level keel. Good thing we installed it."

"You're right!" said Jackson.

Now they were falling earthward with great rapidity, but, thanks to the gyroscope stabilizer, the "side-slipping," than which there is no motion more dreaded by an aviator, had nearly ceased. The craft was volplaning down as it ought, and Tom had it under as perfect control as was possible under the circumstances.

"We'll get down all right if something else doesn't happen," he said to Jackson, with grim humor.

"Well, let's hope that it won't," said the mechanic. "We're a good distance up yet."

They were, as a matter of fact, for the explosion, or whatever had happened to the craft, had occurred at a height of over two miles, and they at once began falling. As yet Tom Swift was unaware of the exact nature of the accident or its cause. All he knew was that there had been a big noise and that the engine had stopped working. He could not see the silencer from where he sat, as it was constructed on the underside of the motor, but he had an idea that the same sort of mishap had occurred as on the occasion when the test machine had sailed through the roof of his workshop.

"But, luckily, this wasn't as bad," mused Tom. "Anyhow the motor is out of business."

And this was very evident. The young inventor had tried to start the apparatus after its stoppage by the explosion, but it had not responded to his efforts, and then he had desisted, fearing to cause some further damage, or, perhaps, endanger his own life and that of Jackson.

Down, down swept Silent Sam—doubly silent now, and Tom began looking about for a good place to make a landing. This was nothing new for either him or his mechanician, and they accepted the outcome as a matter of course.

"Not a very lively place down there," remarked Jackson, as he looked over the side of the cockpit.

"If we have to depend for help on any one down there, I guess we'll be a long time waiting," agreed Tom. They were about to land in a very lonely spot. It was one he had never before visited, though he knew it could not be much more than twenty miles from his own home, as they had not flown much farther than that distance.

But, somehow or other, Tom had not visited this particular section, and knew nothing of it. He saw below him, as Jackson had seen, a lonely stretch of country—a big field, once a wood-lot, evidently, as scattered about were some stumps and some second growth trees. There were also a number of evergreens—Christmas trees Jackson called them. And this was the only open place for miles, the surrounding country being a densely wooded one. There did not appear to be a house or other building in sight where they might seek help.

"But maybe we can make the repairs ourselves and keep on," the lad thought.

With practiced eye he picked out a smooth, grassy, level spot, in the midst of scattered evergreen trees, and there Tom Swift skillfully brought his Air Scout to rest. With a gentle thud the rubber-tired wheels struck the Earth, rolled along a little distance, and then called to a stop.

Hardly had the aeroplane ceased moving when Tom and his companion jumped out and began eagerly to examine the machinery to see the extent of damage.

"I thought so!" Tom exclaimed. "The silencer cracked under the strain. Those exhaust gases have more pressure that I believed possible. I increased the margin of safety on this muffler, too. But she's cracked, and I can't use the machine until I put on a new one. Good thing I didn't ask for a government inspection until after this trial flight."

"That's so," agreed Jackson. "But can't you patch it up, or go on without a muffler, so we can get back home?"

"I'm afraid not," Tom answered. "You see I removed all the old exhaust pipe fittings when I put on my new silencer. Now if I took off my attachment there wouldn't be anything to carry off the discharged gases, and they'd form a regular cloud about us. We couldn't stand it without gas masks, such as they use in the trenches, and we haven't any of those with us."

"That's right," agreed Jackson. "Well, what do you want to do? Have me stay here and guard the machine while you go for help? Or shall I go?"

"I don't know why we both can't go," said Tom. "There is no use trying to patch up this machine here. I'll have to send a truck after it, and dismantle it before I can get it home.

"As for either of us staying here on guard, I don't quite see the need of that. This looks like the jumping-off place to me. I don't believe there's a native within miles. I didn't see any houses as we came down, and I think Silent Sam will be perfectly safe here. No one can run off with him, anyhow. He'd be as hard to start as an automobile with all four wheels gone. Let's leave it here and both walk back."

"All right," agreed Jackson. "That suits me. Might as well leave our togs here, too. It will be easier walking without them," and he began taking off the fur-lined suit, his cap, and his goggles, such as he and Tom wore against the piercing cold of the upper regions.

"We can stuff them in the cockpit and leave them," went on the mechanician, as he divested himself of his garments. As he stowed them away in his seat he gave one more look at the broken muffler. As Tom Swift said, his new silencer had literally blown up, a large piece having been torn from the gas chamber.

Something that Jackson saw caused him to utter an exclamation that brought Tom Swift to his side.

"What is it?" asked the young inventor.

"Look!" was the answer. "See! Just at the edge of that break! It's been filed to make the metal thinner there than anywhere else. You didn't do that, did you?"

"I should say not!" cried Tom. "Why, to file there would mean to weaken the whole structure."

"And that's exactly what's happened!" declared Jackson, as he gave another look. "Some one has filed this nearly through—leaving only a thin metal skin, and when the gas pressure became too much it blew out. That's what happened!"

Tom Swift made a quick but thorough examination.

"You're right, Jackson!" he exclaimed. "That was filed deliberately to cause the accident. And it must have been done lately, for I carefully inspected the silencer when I put it on, and it was in perfect order. There's been spy work here. Some one got into the hangar and filed that casing. Then the accumulated pressure of the gases did the rest."

"As sure as you're alive!" agreed Jackson. "Maybe that's what Gale did when he called."

"No," returned Tom, shaking his head, "he didn't get a chance to do anything like that. I watched him all the while. But perhaps this is what he referred to when he said he and his company would repudiate any act of that spy with the gold tooth—Lydane, so Gale said his name was. Maybe that's what Lydane did."

"He was capable of it," agreed the mechanic, "but he couldn't have done it that time you tripped him into the mud puddle. This silencer wasn't built then."

"No, you're right," assented Tom. "Then he must have been around since, doing some of his tricky work!"

"I don't see how that could have been," said Jackson slowly. "We've kept a very careful watch, and your shop has been specially guarded."

"I know it has," said Tom. "There couldn't much get past Koku; but some one seems to have done it, or else how could that filing have been done?"

Jackson shook his head. The problem was too much for him. He looked carefully at the exploded and broken silencer, and Tom, too, gave it a critical eye. There was no doubt but that it had been filed in several places to weaken the structure of the metal.

"When did you last see that it was in perfect condition?" asked Jackson.

Tom named a certain date.

"That was just before Gale called," observed the mechanician. "He might have known of it."

"I wish I'd known of it at the time," said Tom savagely. "He wouldn't have gotten away as easily as he did. Well, there's no use standing here talking about it. Let's get back to civilization and we'll send back one of the trucks. Luckily I have another silencer I can put on for the government test. This one will never be of any more use, though I may be able to save some of the valves and baffle plates."

Slowly they turned from the disabled aeroplane and started to look for a path that would lead them out of the lonely place. Tom as the first to strike what seemed to be a cow path, or perhaps what had been a road into the wood lot in the early days.

As he tramped along it, followed by Jackson, the young inventor suddenly stopped, as he came to a sandy place, and, stooping over, looked intently at some queer marks in the soil.

"What is it?" asked the mechanician.

"Looks like the marks of an automobile," said Tom slowly. "And I was just trying to remember where I'd seen marks like these before."



CHAPTER XXI

THE DESERTED CABIN

For several seconds the young inventor remained bending over the queer marks in that little sandy path of the lonely field in the midst of the silent woods. Jackson watched him curiously, and then Tom straightened up, exclaiming as he did so:

"I have it! Now I know where it was! I saw marks like these the night Mr. Nestor disappeared. Mr. Damon and I noticed the marks in the dust on the road the time we made the forced landing the first night we tried out the silent motor. That's it! They are the same marks! I'm sure of it!"

"I wouldn't go so far as to say that," said Jackson slowly. He was more deliberate than Tom Swift, a fact for which the young inventor was often glad, as it saved him from impulsive mistakes.

"This may not be the same auto," went on the mechanician. "I'll admit I never saw square tire marks like those before. Most of the usual ones are circular, diamond-shape or oblong. Some tire manufacturer must have tried a new stunt. But as for saying these marks were made by the same machine you saw evidences of the night Mr. Nestor disappeared, why, that's going a little too far, Tom."

"Yes, I suppose it is," admitted the young inventor. "But it's a clew worth following. Maybe Mr. Nestor has been brought to some lonely place like this, and is being held."

"Why would any one want to do that?" asked Jackson. "He had no enemies.

"Well, perhaps those who ran him down and injured him are afraid to let him go for fear he will prosecute them and ask for heavy damages," suggested Tom. "They may be holding him a captive until he gets well, and aim on treating him so nicely that he won't bring suit."

"That's a pretty far-fetched theory," said the mechanician as he carefully looked at the tracks. "But of course it may be true. Anyhow, these tire marks are rather recent, I should say, and they are made by a new tire. Do you think we can follow them?"

"I'm going to try!" declared Tom. "The only trouble is we can't tell whether it was going or coming—that is we don't know which way to go."

"That's so," agreed his companion. "And so the only thing to do is to travel a bit both ways. The path, or road, or whatever you call it, is plainly enough marked here, though you can't always pick out the tire marks. They show only on bare ground. The grass doesn't leave any tracks that we can see, though doubtless they are there.

"But as for thinking this car is the same one the marks of which you saw on the lonely moor, the night you heard the call for help—that's going too far, Tom Swift."

"Yes, I realize that. Of course there must be more than one car with tires which have square protuberances. But it's worth taking a chance on—following this clew."

"Oh, sure!" agreed Jackson.

"The only question is, then, which way to go," returned Tom.

They settled that, arbitrarily enough, by going on in the direction they had started after leaving the stranded airship. They followed a half-defined path, and were rewarded by getting occasional glimpses on bare ground of the odd tire marks.

Through a devious winding way, now hidden amid a lane of trees, and again cutting across an open space, the path led. They saw the marks often enough to make sure they were on the right trail, and in one place they saw several different patches of the odd marks.

They went on perhaps half a mile more, when they came to a lonely road and saw where the car had turned from that into the wood-lot, as Tom called the place where his craft had settled down.

"Look!" cried the young inventor to Jackson. "They've been here more than once, and have gone along the road in both directions. They seem to have used this turning into the lot as a sort of stopping place."

This was plain enough from an examination of the marks in the sandy soil of the road, which was one not often used. The automobile with the queer, square marks on the tires had turned into the lot, coming and going in both directions.

"This settles it!" cried Tom, when he finished making an examination. "There's something farther back in this lot that we've got to see. This auto has been coming and going, and we should have followed the tracks the other way from the point where we first saw them, instead of coming this way."

"Except that we've learned the place of departure," suggested Jackson. "Evidently the wood-lot is a blind alley. The car goes in, but it can come out only just at this point, or, at least, it does."

"That's right!" agreed Tom. "Now the thing to do is to follow our track back to where we started. There must be some place where the car went to—some headquarters, or meeting place with some one, farther back in the lot. If we can only follow the trail back as well as we did coming, we may find out something."

"Well, let's try, anyhow," suggested Jackson.

They had no difficulty in making their way back to the spot where they had first seen the queer marks. But from then on their task was not so easy. For sandy or bare patches of earth were not frequent, and they had to depend on these to give them direction, for the road was overgrown and not well defined.

Often they would search about for some time after leaving one patch of the marks before they found another that would justify them in keeping on.

"They have headquarters, or a rendezvous, somewhere back in this lot!" declared Tom, as they hurried on. "I think we're on the track of a mystery."

"Unless it turns out that some farmer has treated himself to an auto with new tires of square tread, and is hauling wood," said Jackson. "It may turn out that way."

"Yes, it may," agreed Tom. "But, taking everything into consideration, I think we're on the verge of finding out something. Even if we do discover that the owner of this auto is only hauling wood, he may be able to help us to a clew as to the whereabouts of Mr. Nestor."

"How?"

"Well, maybe he was in his machine on the moor the night the call for help came. He may even have aided to carry Mr. Nestor away. And if he doesn't know a thing about it—which, of course, is possible—the man who bought these queer tires can tell us who makes them, or who deals in them, and we can find out what autoists around here have their cars equipped with this odd tread."

"Yes," agreed Jackson, "that can be done."

And so they kept on, scouting here and there to either side of the half-defined path, until they were far back from the spot where they had left the Air Scout.

"We don't appear to be getting any warmer, as the children say," remarked Jackson, as he straightened up and looked about, for his back ached from so much stooping over to look for the odd marks.

"We haven't seen anything yet, I'll admit," said Tom. "But it won't be dark for another hour or so, and I vote that we keep on."

"Oh, I wasn't thinking of giving up!" exclaimed Jackson. "If there's anything here—at the end of the route, as you might say—we'll find it. Only I hope it doesn't turn out to be just a wood pile, from which some farmer has been hauling logs."

"That would be a disappointment," assented Tom.

The day was waning, and they realized that they ought not to spend too much time on what might turn out to be a wild goose chase. They were in a lonely neighborhood, and while they were not at all apprehensive of danger, they felt it would be best to get to shelter before dark.

"We'll want to send word to Mr. Swift that we're all right."

"Yes," said Tom, "I'd like to get to a place where I can telephone to him or Mrs. Baggert. Well, if we don't find something pretty soon we'll have to turn back. I must complete work on the new motor, for if I'm to offer it to Uncle Sam for air scout purposes, the sooner I can do so the better. Things are getting pretty hot over in Europe, and if ever the United States needed aircraft on the western front they need them now. I want to help all I can, and I also want to help Mary—you understand—Miss Nestor."

"I understand," said Jackson simply. "I only hope you can help her. But I'm afraid—this may turn out to be nothing—following these marks, you know."

"And yet," said Tom slowly, "it would be strange if it was only a coincidence—the two tire marks being the same—the night Mr. Nestor disappeared and now."

And so they kept on, hoping.

The half-defined path through the wood-lot led them in a series of turns and twists, and it extended through a dense patch of woods, growing thickly, where it was so dark that it seemed as if night had fallen.

"We can't spend much more time here," said Tom. "If we don't find something in the next half mile we'll go back and take up the search to-morrow. I'm going to find out what's at the end of this road—even if it's only a wood pile."

For ten minutes more the two went on, making sure, by occasional glimpses at the marks, that they were on the right track. Then, suddenly, they saw something which made them feel sure they had reached their goal.

In a clearing among the trees was a little cabin—a shack of logs—and from the appearance it was deserted. There was not a sign of life around.



CHAPTER XXII

CLEWS AT LAST

For a moment, at sight of the deserted cabin, staring at Tom and his friend, as it were, from its hiding place amid the trees, the young inventor and his companion did not move. They just stood looking at the place.

"Well," said Tom, at length, "we found it, didn't we?"

"We found something anyhow," agreed Jackson. "Whether it amounts to anything or not, we've got to see."

"Come on!" cried Tom, impulsively. "I'm going to see what's there."

"There doesn't appear to be much of anything," said Jackson, as he looked toward the lonely cabin with critical eyes. "I should say that place hadn't been used, even as a chicken coop, in a long while."

"We can soon tell!" exclaimed Tom, striding forward.

"Wait just a minute!" cried his companion, catching him by the coat. "Don't be in such a hurry."

"Why not?" asked Tom. "There isn't any danger, is there?"

"I don't know about that. There's no telling who may be hidden in that cabin, in spite of its deserted appearance. And though there aren't any 'No Trespass' signs up, it may be that we wouldn't be welcome. If there are some tramps there, which is possible, they might take a notion to shoot at us first and ask questions as to our peaceable intentions afterward—when it would be too late."

"Nonsense!" exclaimed Tom. "There aren't any tramps there and, if there were, they wouldn't dare shoot. I'm going to see what the mystery is—if there is one."

But there was no sign of life, and, taking this as an indication that their advance would not be disputed, Jackson followed Tom. The latter advanced until he could take in all the details of the shack. It was made of logs, and once had been chinked with mud or clay. Some of this had fallen out, leaving spaces between the tree trunks.

"It wasn't a bad little shack at one time," decided Tom. "Maybe it was a place where some one camped out during the summer. But it hasn't been used of late. I never knew there was such a place around here, and I thought I knew this locality pretty well."

"I never heard of it, either," said Jackson. "Let's give a shout and see if there's any one around. They may be asleep. Hello, there!" he called in sufficiently vigorous tones to have awakened an ordinary sleeper.

Put there was no answer, and as the shadows of the night began to fall, the place took on a most lonely aspect.

"Let's go up and knock—or go in if the door's open," suggested Tom. "We can't lose any more time, if we're to get out of here before night."

"Go ahead," said Jackson, and together they went to the cabin door.

"Locked!" exclaimed Tom, as he saw a padlock attached to a chain. It appeared to be fastened through two staples, driven one into the door and the other into the jamb, at right angles to one another and overlapping.

"Knock!" suggested Jackson. But when Tom had done so, and there was no answer, the machinist took hold of the lock. To his own surprise and that of Tom, one of the staples pulled out and the door swung open. The place had evidently been forced before, and the lock had not been opened by a key. The staple had been pulled out and replaced loosely in the holes.

For a moment nothing could be made out in the dark interior of the shack. But as their eyes became used to the gloom, Tom and his companion were able to see that the shack consisted of two rooms.

In the first one there was a rusty stove, a table, and some chairs, and it was evident, from pans and skillets hanging on the wall, as well as from a small cupboard built on one side, that this was the kitchen and living room combined.

"Anybody here?" cried Tom, as he stepped inside.

Only a dull echo answered.

The two could now see where a door gave entrance to an inner room, and this, a quick glance showed, was the sleeping apartment, two bunks being built on the side walls.

"Well, somebody had it pretty comfortable here," decided Tom, as he looked around. "They've been cooking and sleeping here, and not so very long ago, either. It wouldn't be such a bad place if it was cleaned out."

"That's right," agreed Jackson. "Wouldn't mind camping here myself, if there was any fishing near."

"The river can't be far away," suggested Tom. "And now let's see what we can find, and see if we can get a line on who has been here. But first we'll let in a little light."

He opened a window in the sleeping room, and pushed back the heavy plank shutter that had been closed. When the light entered it was seen that both bunks bore evidence of having been lately slept in. The blankets were tossed back, as if the occupants had risen, and in the outer room, on the stove, were signs that indicated a meal had been served not many days gone by.

"Now," observed Tom musingly, as he wandered about the place, "if we could only find out who owns this, and who has been here lately—"

Jackson stooped over, and, thrusting aside an end of the blankets that trailed on the floor from one of the bunks, picked up something.

"What is it?" asked Tom.

"Looks like a leather pocketbook," was the answer. "That's what it is," the mechanic went on, as he held the object to the light. "It's a wallet."

"Let me see it!" exclaimed Tom quickly. He took the wallet from the hands of Jackson. Then the young inventor uttered a cry. "A clew at last!" he exclaimed. "A clew at last! Mr. Nestor has been in this cabin!"

"How do you know?" asked Jackson quickly.

"This is his wallet," said Tom excitedly. "I've often seen him have it. In fact he had it with him on Earthquake Island, the time I sent the wireless message for help. I saw it several times then. He kept in it what few papers he had saved from the wreck. And I've seen it often enough since. That's Mr. Nestor's wallet all right. Besides, if you want any other evidence—look!" He opened the leather flaps and showed Jackson on one, stamped in gold letters, the name of Mary's father.

"Well, what do you make of it, Tom?" asked the mechanician, as he finished his examination of the wallet. "What does it mean? The pocket-book is empty and that—"

"Might mean almost anything," completed Tom. "But it's a clew all right! He's been here, and I'm pretty certain he was brought here in the auto with the odd tires—the one Mr. Damon and I saw traces of the night we heard the cries for help."

"But that doesn't help us now," said Jackson. "The point is to find out how lately Mr. Nestor was here, and what has happened to him since. There isn't anything in the wallet, is there?"

"Nothing," answered Tom, making a careful examination so as to be sure. "It's as empty as a last year's bird nest. He's been robbed—that's what has happened to Mr. Nestor. He was waylaid that night, instead of being run down as I thought—waylaid and robbed and then his body was brought here."

"There you go again, Tom! Jumping to conclusions!" said Jackson, with a friendly smile, and with the familiarity of an old and valued helper. "Maybe he's in perfectly good health. Just because you found his empty wallet doesn't argue that your friend is in serious trouble. He may have dropped this on the road and some one picked it up. I'll admit they may have taken whatever was in it, but that doesn't prove anything. The thing for us to do is to find out who knows about this shack; who owns it, on whose land it is, and whether any one has been seen here lately."

"They've been here lately whether they've been seen or not," said Tom positively. "There are the auto tracks. It rained two days ago, and the tracks were made since. Mr. Nestor must have been here within two days."

"He may or may not," said Jackson. "Say, rather, that some one was here and left his wallet after him. Now see if we can find other clews!"

They looked about in the fast fading light, but at first could discover nothing more than evidences that three or four persons had been living in the shack and at some recent date—probably within a day or two.

They had had their meals there and had slept there. But this seemed to be all that could be established, other than that Mr. Nestor's wallet was there, stripped of its contents.

Tom was looking through the closet, from which a frightened chipmunk sprang as he opened the door. There were the remains of some food, which accounted for the presence of the little striped animal. And, as Tom poked about, his hand came in contact with something wrapped in paper on an upper shelf. It was something that clinked metallicly.

"What's that?" asked Jackson. "Knives, or some other weapons?"

"Neither," answered Tom. "It's a couple of files, and they've been used lately. I can see something in the grooves yet and—"

Suddenly Tom ceased speaking and drew from his pocket a small but powerful magnifying glass. Through this he looked at one of the files, taking it out in front of the shack where the light was better.

"I thought so!" he cried. "Look here, Jackson!"

"What is it?"

"Another clew!" answered Tom.



CHAPTER XXIII

THE GOVERNMENT TEST

For a moment Jackson thought Tom had discovered a clew to, or evidences of, some crime. He had an unpleasant suspicion, for an instant, that there was blood on the files, and that it might prove to be the blood of Mr. Nestor.

But the satisfaction that showed on Tom's face did not seem to indicate such dire possibilities as these.

"What is it?" asked Jackson, unable to guess at what Tom was looking through the powerful glass. "What do you see?"

"Metal filings on the grooves of these files," said the young inventor. "And, unless I'm greatly mistaken, the particles of filings are from the case of my aircraft silencer!"

"What!" cried the machinist. "Do you mean those are the files used in weakening the outer case of your new machine, so that it burst a little while ago?"

"That what I think," answered Tom. "I know it sounds pretty far-fetched," he went on. "But take a look for yourself. If those particles on, the files aren't exactly of the same color and texture as the material of which the silencer case is made, I'll never build another machine."

Jackson peered through the powerful glass moving out a little farther from the shack, so as to get the best light possible on the subject of his examination. It was fast getting dark, but there was enough glow in the western sky for his purpose.

"Am I right?" asked Tom.

"You're right!" declared his helper. "This is exactly the same metal as that of which your silencer case is made. It's a peculiar mixture of aluminum and vanadium steel. I never knew it used in any shop but yours, and these filings are certainly of that metal. It would seem, Tom, that these were the files used to cut a crease in the case of your silencer to weaken it so it would burst."

"My idea exactly!" cried Tom. "The spy, who got into my shop in some undiscovered manner, did his work and then fled here to hide. He left his files behind. Mr. Nestor must have been here, either before or after. No, I'll not say that, either. Finding his wallet here doesn't prove that he was here. It might have been brought here by one of the spies and dropped. But I'm sure we're on the track of the men who damaged my airship, as well as those who know something of the mystery of Mr. Nestor."

"I agree with you," said Jackson. "Of course there's a possibility that the same peculiar metal you used in your silencer case may have been used in some other machine shop, and these files may have come from there, and have been employed in perfectly regular work. But the chances are—"

"There's only one way to make sure," said Tom. "Let's take the files with us and see if they fit in the grooves where the break came. We'll take these back to where we left the Air Scout," and he clinked the files he held.

"We can just about make it before it gets black dark," returned Jackson. "But that won't give us any more time to look around here," and he indicated the hut.

"I fancy we've seen all there is to see here," said Tom. "Mr. Nestor isn't here, and whether he was or not is a question. Anyhow, some one was here who had something to do with him after his disappearance, I'm positive of that. And I'm sure some one was here who damaged my airship. Now we'll run down both those clews, find out who owns this place, who has been using it, and all we can along that line. So, if you're ready, let's travel."

The two set out to make their way back to where they had left the stranded airship. It was fast becoming dark, but they could hurry along with more speed now, as they did not have to stop to look for the marks of the peculiar automobile tires. They had noticed the path along which they had traveled, and in half the time they had spent coming they were back where the Air Scout rested undisturbed in the meadow amid the trees.

Making sure that, as far as they could tell, no one had visited the craft since they had left it, Tom and Jackson compared the file marks on what was left of the broken silencer case with the files they had found in the hut. They used a small, but powerful electric lamp to aid them in this examination, as it was too dark to see otherwise, and what they saw caused the young inventor to exclaim:

"That settles it! These were the files used!"

"That's right!" agreed his assistant. "You've called the turn, Tom. The next thing to do is to find who connects with the files."

"Yes. To do that and find Mr. Nestor," said Tom. "We have plenty of work ahead of us. But let's get nearer civilization and send some word to the folks at home. They'll be getting worried."

"It doesn't seem as if there was a way out of here without using an airship," remarked Jackson.

But he and Tom finally reached the seldom-used road which ran along the field that contained the lonely shack, and, following this, they reached a farmhouse about a mile farther on. Greatly to their relief, there was a telephone in the place. True it was only a party line, set up by some neighboring farmers for their own private use, but one of the subscribers, to whose home the private line ran, had a long distance instrument, and after a talk with him, this man promised Tom to call up Mr. Swift and acquaint him with the fact that his son and Jackson were all right, and would be home later.

"And now," said Tom, after thanking their temporary host, a farmer named Bloise, "can you tell us anything about an old cabin that stands back there?" and he indicated the location of the mysterious shack.

"Well, yes, I can tell you a little about it, but not very much," said Mr. Bloise. "It was built, some years ago, by a rich New Yorker, who bought up a lot of land around here for a game preserve. But it didn't pan out. This cabin was only the start of what he was going to call a 'hunting lodge,' I believe it was. There was to be a big building on the same order, but it never was built.

"Some say the fellow lost all his money in Wall Street, and others say the state wouldn't let him make a game preserve here. However it was, the thing petered out, and the old shack hasn't been used since."

"Oh, yes, it has!" exclaimed Tom. "We just came from there, and there are signs which show some one has been sleeping there and eating there."

"There has!" exclaimed the farmer. "Well, I didn't know that."

"I did," said his son, a young man about Tom's age. "I meant to speak of it the other day. I saw an automobile turn into the old road that the men used when they built the shack. I thought it was kind of queer to see a touring car turn in there, and I meant to speak of it, but I forgot. Yes, some one has been at the old cabin lately."

"Do you know who they are?" asked Tom eagerly. "We are looking for a Mr. Nestor, who disappeared mysteriously about two weeks ago, and I just found his wallet there in the shack!"

"You did!" exclaimed Mr. Bloise. "That's queer! You relatives of this Mr. Nestor?" he asked.

"Not exactly," Tom answered. "Just very close friends."

"Well, it's too bad about his being missing in that way," went on the farmer. "I read about it in the paper, but I never suspected he was around here."

"Oh, we're not sure that he was," said Tom quickly. "Finding his wallet doesn't prove that," and he told the story of his own and Jackson's appearance on the scene, to the no small wonder of the farmer and his family. Tom said nothing about the finding of the files, nor the evidence he deduced from them. That was another matter to be taken up later.

"Who were in the auto you saw?" asked Tom of the farmer's son. "Was Mr. Nestor in the car?"

"I couldn't be sure of that. There were two men in the machine, and they were both strangers to me. They were talking together, pretty earnestly, it seemed to me."

"One did not appear as if he was being taken away against his will, did he?" asked Tom.

"No, I can't say that he did," was the answers "They looked to me, and acted like, business men looking over land, or something like that. They just turned in on the road that leads to the old hunting cabin, as we call it around here, and didn't pay any attention to me. Then I forgot all about them."

"Neither of them could have been Mr. Nestor," decided Tom. "At least it doesn't seem as if he'd talk at all companionably to a man who had treated him as we think Mr. Nestor has been treated. I guess that clew isn't going to amount to much."

"It may!" insisted Jackson. "They may have had Mr. Nestor in the car all the while—concealed in the back you know. We've got to find out more about these men and their auto, Tom."

"Well, yes, perhaps we have. But how?"

"Station some one at the shack, or at the beginning of the private road. The men may come back."

"That's so—they may. We'll do that!" cried the young inventor. "We must tell the police and Mr. Nestor's folks what we have learned. How can we get back to Shopton in a hurry?" he asked the farmer.

"Well, I can drive you to the railroad station," was the answer.

"Thank you," remarked Tom. "We'll accept your offer. And as soon as we get back we must send some one from the shop to stand guard over the airship," he added in an aside to Jackson. "Those file fellows may come back."

"That's so, we can't take any chances."

The farmer soon had his team at the door, and, after they had had a hasty but satisfying supper at the farmhouse, the son drove Tom and Jackson several miles to a railroad station, where they could catch a train for Shopton.

In due season Tom's home was reached. He intended to stop but a minute, to assure his father that everything was all right, and then get out his speedy runabout to go to see Mary, to tell her the news.

But when Tom sought his father in the library, he was told that there was a visitor in the house.

"Tom," said his father, "this gentleman is from Washington. He wants to arrange for a government test of your silent airship. I told him I thought you were about ready for it."

"A government test!" cried Tom. "Why, I didn't think the government even knew I was working on such an idea!" Tom was greatly surprised.



CHAPTER XXIV

IN THE MOONLIGHT

With a reassuring smile the visitor from Washington looked at Tom Swift.

"The government officials," he said, "know more than some people give them credit for—especially in these war times. Our intelligence bureau and secret service has been much enlarged of late. But don't be alarmed, Mr. Swift," went on the caller, whose name was Mr. Blair Terrill. "Your secret is safe with the government, but I think the time is ripe to use it now—that is, if you have perfected it to a point where we can use it."

"Yes," answered Tom slowly, "the invention is practically finished and it is a success, except for a few minor matters that will not take long to complete.

"Our accident this afternoon had nothing to do with the efficiency of the silencer," Tom went on. "It was deliberately damaged by some spy. I'll take that up later. That I am interested to know how you heard of my Air Scout, as I call it."

"Well, we have agents, you know, watching all the inventors who have helped us in times past, and we haven't forgotten your giant cannon or big searchlight. I might say, to end your curiosity and lull your suspicions, that your friend, Ned Newton, who has been doing such good Liberty Bond work, informed us of your progress on the silent motor."

"Oh, so it was Ned!" exclaimed Tom.

"Yes. He told us the time was about ripe for us to make you an offer for your machine. I think we can use it to great advantage in scout work on the western front," went on the agent, and he soon convinced Tom that when it came to a knowledge of airships, he had some very pertinent facts at his disposal.

"When can you give me a test?" Mr. Terrill asked Tom.

"As soon as I can get my craft back to the shop and fit on a new outer case. That won't take long, as I have some spare ones. But I must help the Nestors," he went on, speaking to his father. "I didn't mention it over the wire," he added, "but we've found in the cabin a clew to the missing man. I must tell Mary and her mother, and help them all I can."

"And allow me to help, too," begged Mr. Terrill. "Since this affects you, Mr. Swift, and since you are, in a way, working for Uncle Sam, you must let him help you. This is the first I have heard of the missing gentleman, of whom your father just told me something, but you must allow me to help search for him. I will get the United States Secret Service at work."

"That will be fine!" cried Tom. "I wanted to get their aid, but I didn't see how I could, as I knew they were too busy with army matters and tracing seditious alien enemies, to bother with private cases. I'm sure the Secret Service men can get trace of the persons responsible for the detention of Mr. Nestor, wherever he is."

"They'll do their best," said Mr. Terrill. "I'm a member of that body," he went on, "and I'll give my personal attention to the matter."

Then followed a busy time. Tom did not get to bed until nearly morning. For he had to arrange to send some of his men to guard the stranded airship, and then he went to see Mary and her mother, taking them the good news that the search for Mr. Nestor would be prosecuted with unprecedented vigor.

"If it isn't too late!" sadly said the missing man's wife.

"Oh, I'm sure it isn't!" declared Tom.

In addition to sending a guard to the airship, other men, some of them hastily summoned from the nearest federal agency, were sent to keep watch in the vicinity of the lonely cabin. They had orders to arrest whoever approached, and a relay of the men was provided, so that watch could be kept up night and day. Besides this, other men from the Secret Service began scouring the country around the locality of the cabin, seeking a trace of the two persons the farmer's son had seen in the automobile.

"If Mr. Nestor is to be found, they'll find him!" declared Tom Swift.

Mr. Damon, as might be expected, was very much excited and wrought up over all these happenings.

"Bless my watch chain, Tom Swift!" cried the eccentric man, "but something is always happening to you. And to think I wasn't along when this latest happened!"

"Well, you can be in at the finish," promised Tom, and it was strange how his promise was fulfilled.

Meanwhile there was much to do. During the time the Secret Service men were busy looking up clews which might lead to the finding of Mr. Nestor and keeping watch in the vicinity of the hut, Tom had his airship brought back to the hangar, and a new silencer was attached. While this work was going on the place was guarded night and day by responsible men, so there was no chance for an enemy spy to get in and do further damage.

An investigation was made of the Universal Flying Machine Company, but nothing could be proved to link them with the outrage. Gale and Ware were in Europe—ostensibly on government business, but it was said that if anything could be proved connecting them with the attempt made on Tom Swift's craft, they would be deprived of all official contracts and punished.

All this took time, and the waits were wearisome, particularly in the case of Mr. Nestor. No further trace of him was found, though every effort was made. Tom began to feel that his boast of his enemies having to get up early in the morning to get ahead of him, had been premature, to say the least.

Tom Swift worked hard on his new Air Scout. He determined there would be nothing lacking when it came to the government test, and not only did he make sure that no enemy could tamper with his machine, but he took pains to see that no inherent defect would mar the test.

Jackson and the other men helped to the best of their ability, and Mr. Swift suggested some improvements which were incorporated in the new machine.

One of the puzzles the Secret Service men had to solve was that of the connection, if any, between the men who had to do with the missing Mr. Nestor and those who had damaged Tom's airship by filing the muffler case so it was weakened and burst. That there was some connection Tom was certain, but he could not work it out, nor, so far, had the government men.

At last the day came when the big government test was to be made. Tom had completed his Air Scout and had refined it to a point where even his critical judgment was satisfied. All that remained now was to give Mr. Terrill a chance to see how silently the big craft could fly, and to this end a flight was arranged.

Tom had put the silencer on a larger machine than the one he and Jackson had used. It held three easily, and, on a pinch, four could be carried. Tom's plan was to take Mr. Damon and Mr. Terrill, fly with them for some time in the air, and demonstrate how quiet his new craft was. Then, by contrast, a machine without the muffler and the new motor with its improved propellers would be flown, making as much noise as the usual craft did.

"I only wish," said Tom, as the time arrived for the official government test, "that Mary could be here to see it. She was the one who really started me on this idea, so to speak, as it was because I couldn't talk to her that I decided to get up a silent motor."

But Mary Nestor was too grief-stricken over her missing father to come to the test, which was to take place late one afternoon, starting from the aerodrome of the Swift plant.

"First," said Tom, to Mr. Terrill, "I'll show you how the machine works on the ground. I'll run the motor while the plane is held down by means of ropes and blocks. Then we'll go up in it."

"That suits me," said the agent. "If it does all you say it will do, and as much as I believe it will do, Uncle Sam will be your debtor, Mr. Swift."

"Well, we'll see," said Tom with a smile.

Preparations were made with the greatest care, and Tom went over every detail of the machine twice to make certain that, in spite of the precautions, no spy had done any hidden damage, that might be manifested at an inopportune moment. But everything seemed all right, and, finally, the motor was started, while Mr. Terrill, and some of his colleagues from the Army Aviation department looked on.

"Contact!" cried Tom, as Jackson indicated that the compression had been made.

The mechanic nodded, gave the big propeller blades a quarter turn and jumped back. In an instant the motor was operating, and the craft would have leaped forward and cleaved the air but for the holding ropes and blocks. Tom speeded the machinery up to almost the last notch, but those in the aerodrome hardly heard a sound. It was as though some great, silent dynamo were working.

"Fine!"

"Wonderful!"

"Wouldn't have believed it possible!"

These were some of the comments of the government inspectors.

"And now for the final test—that in the air," said Mr. Terrill.

Previous to this he and his colleagues had made a minute examination of the machinery, and had been shown the interior construction of the silencer by means of one built so that a sectional view could be had. Tom's principles were pronounced fundamental and simple.

"So simple, in fact, that it is a wonder no one thought of it before," said a navy aviation expert. "It is the last word in aircraft construction—a silent motor that will not apprise the enemy of its approach! You have done wonders, Mr. Swift!"

"I'd rather hear you say that after the air test," replied Tom, with a laugh. "Are you ready, Mr. Terrill?"

"Whenever you are."

"How about you, Mr. Damon?"

"Oh, I'm always ready to go with you, Tom Swift. Bless my trench helmet, but you can't sail any too soon for me!"

There was a genial laugh at his impetuosity, and the three took their seats in the big craft. Once more the engine was started. It operated as silently as before, and the first good impressions were confirmed. Even as the machine moved along the ground, just previous to taking flight into the air, there was no noise, save the slight crunch made by the wheels. This, of course, would be obviated when Silent Sam was aloft.

Up and up soared the great craft, with Tom at the engine and guide controls, while Mr. Terrill and Mr. Damon sat behind him, both eagerly watching. Mr. Terrill was there to find fault if he could, but he was glad he did not have to.

"The machine works perfectly, Mr. Swift," he said. "My report cannot be otherwise than favorable."

"We mustn't be in too much of a hurry," said Tom, who had learned caution some time ago. "I want to sail around for several hours. Sometimes a machine will work well at first, but defects will develop when it is overheated. I'm going to do my best to make a noise with this new motor."

But it seemed impossible. The machinery worked perfectly, and though Silent Sam took his passengers high and low, in big circles and small ones, there was no appreciable noise from the motor. The passengers could converse as easily, and with as little effort, as in a balloon.

"Of course that isn't the prime requisite," said Mr. Terrill, "but it is a good one. What we want is a machine that can sail over the enemy's lines at night without being heard, and I think this one will do it—in fact, I'm sure it will. Of course the ability of the passengers to converse and not have to use the uncertain tube is a great advantage."

As Tom Swift sailed on and on, it became evident that the test was going to be a success. The afternoon passed, and it began to grow dark, but a glorious full moon came up.

"Shall I take you down?" the young inventor asked Mr. Terrill.

"Not quite yet. I thoroughly enjoy this, and it isn't often I get a chance for a moonlight airship ride. Go a little lower, if you please, and we'll see if we attract any attention from the inhabitants of the earth. We'll see if they can possibly hear the machine, though I don't see how they can."

And they did not. Tom piloted the machine over Shopton, sailing directly over the center of the town, where there was a big crowd walking about. Though the airship sailed only a few hundred feet above their heads, not a person was aware of it, since the craft's lights were put out for this test.

"That settles it," said Mr. Terrill. "You have succeeded, Tom Swift!"

But Tom was not yet satisfied. He wanted a longer test. Hardly knowing why he did it he sent the craft in the direction of Mary Nestor's home. As he sailed across her lawn he saw, in the moonlight, that she and her mother were walking in the garden. They did not look up as the aircraft passed over their heads, and were totally unaware of its presence, unless they caught a glimpse of it as it flitted silently along, like some great bird of the night.

"It is perfectly wonderful!" declared Mr. Terrill, and he spoke in ordinary tones, that carried perfectly to the ears of Tom and Mr. Damon.

"Wonderful!" cried the eccentric man. "Bless my chimney, but it's the greatest invention in the world! Yes, it is! Don't tell me it 'isn't!"

And no one did.

Passing the Nestor home, the saddened occupants of which were unaware of the passage, Tom sent the Air Scout about in a circle, intending to proceed to the hangar. And then, some whim, perhaps, caused him to guide Silent Sam out toward the lonely hut. Mr. Damon and Mr. Tenrill seemed perfectly content to sail on and on indefinitely in the moonlight. Tom thought he would take them over a lonely neighborhood, and then bring them back.

In a little while the craft was directly over the stretch of country where the aeroplane accident bad occurred, and where Tom and Jackson had found the deserted hut.

Rather idly Tom looked down, wondering if the Secret Service men were on the watch and if they had discovered anything.

Suddenly Tom was aware of an automobile moving along the field path toward the cabin. There were two men in the car, both on the front seat, and as Tom looked down the brilliant moonlight showed him the figure of another man, behind, and huddled in the tonneau of the car. The aeroplane was low enough for all these details to be seen by the moon's gleam, but the men in the car, not hearing any noise, did not look up, so they were unconscious of this aerial espionage.

"Look! Look!" exclaimed Tom in a low voice to his companions. "Doesn't that seem suspicious?"



CHAPTER XXV

THE GOLD TOOTH

Eagerly Mr. Damon and the government agent leaned over and looked down. In the moonlight they saw the same sight that had attracted Tom Swift. The touring car, the two men in front, and the huddled, bound figure in the back.

"Can you go down, Tom, without letting them hear you?" asked Mr. Damon, using a low voice, as if fearful the men in the automobile would hear him.

"I guess so," answered the young inventor. "I can land nearer to the cabin than Jackson and I did, and then we can see what these fellows are up to. It looks suspicious to me. That is, unless they're some of the Secret Service men, and have made a capture," he added to Mr. Terrill.

"Those aren't any of Uncle Sam's men," declared the agent. "That is, unless the bound one is. I can't see him very well. Better go down, and we'll see if we can surprise them."

"My plan," voiced Tom.

Quickly he shifted the rudder, and then, shutting off the motor, as he wanted to volplane down, he headed his craft for an open spot that showed in the bright moonlight. By this time the automobile and its occupants were out of sight behind a clump of trees, but Tom and his companions felt sure of the destination of the men—the deserted cabin in the wood.

As silently as a wisp of grass falling, the big craft came down on a level spot, and then, leaping out, the young inventor and his two companions crept along the path toward the cabin. Mr. Terrill was armed, Tom carried a flashlight, while Mr. Damon picked up a heavy club.

As soon as he came near a place where he thought the marks of the automobile wheels would show, Tom flashed his light.

"I thought so!" he exclaimed, as he saw the square, knobby tread marks left by the tires. "It's the same gang, or some of them in the same car. If we can only capture them!"

"The Secret Service men ought to do that," returned Mr. Terrill, but, as it developed later, they were not on hand, though through no fault of theirs.

On and on crept Tom and the two men, until they came within sight of the cabin. They saw a light gleaming in it, and Tom whispered:

"Now we have them! Work our way up quietly and make them surrender, if we find they're what we think."

"Is there a rear door?" asked Mr. Terrill in a whisper.

Tom answered in the negative, and then all three, in fan shape, crept up to the front portal. It was open, and silently reaching a place where they could make an observation, Tom and his companions looked in.

What they saw filled them with wild and righteous rage, and brought to an end the mystery of the disappearance of Mr. Nestor. For there he sat, bound in a chair, and at a table in front of him were two forbidding-looking men.

"What do you intend to do now?" asked Mr. Nestor in a faint voice. "I cannot stand this captivity much longer. You admit that you don't want me—that you never wanted me—so why do you keep me a prisoner? It cannot do the least good."

"There's no use going over that again!" exclaimed the harsh voice of one of the men. "We told you that if you will promise to keep still about what happened to you, and not to give the police any information about us, we'll let you go gladly. We don't want you. It was all a mistake, capturing you. You were the wrong man. But we re not going to let you go and have you set the police on us as soon as you get a chance. Give us your promise to say nothing, and we'll let you join your friends. If you don't—"

"Make no promises, Mr. Nestor!" cried Tom Swift in a ringing voice, as he leaped from his hiding place, followed by his companions. "Your friends are here, and you can tell them everything!"

"Up with 'em!" called Mr. Terrill to the two conspirators as he confronted them with his automatic pistol ready for firing. He had no need to mention hands—they knew what he meant and took the characteristic attitude.

"Tom! Tom Swift!" cried Mr. Nestor, struggling ineffectually at his bonds. "Is it really you?"

"Well, I hope it isn't any imitation," was the grim answer. "We'll tell you all about it later. Jove, but I'm glad we found you! If it hadn't been for Silent Sam we might never have been able to."

"Well, I don't know who Silent Sam is," said Mr. Nestor faintly. "But I'm sure I'm much obliged to him and your other friends. It has been very hard. Tell me, are my wife and Mary all right?"

"In good health, yes, but, of course, worrying," said Tom. "We saw them in the garden a little while ago. Now don't talk until I set you free."

And as Tom cut the ropes from Mr. Nestor, Mr. Damon used them to bind the two conspirators, while Mr. Terrill stood guard over them. And when they were safely bound, and Mr. Nestor had somewhat recovered from the shock, Tom had a chance to examine the prisoners.

"What does it all mean? Who are you fellows, anyhow, and what's your game?" he demanded.

"Guess it—since you're so smart!" snapped one.

And no sooner had he opened his mouth and Tom had a glance of something gleaming brightly yellow, than the young inventor cried:

"The gold tooth! So it's you again, is it, you spy?"

The man shrugged his shoulders with an assumption of indifference. And, as Tom took a closer look, he became aware that the man was surely none other than Lydane, the spy he had chased into the mud puddle some weeks before. His companion was a stranger to Tom.

"What does it all mean, Mr. Nestor?" asked Tom. "Have these men held you a prisoner ever since you called for help on the moor that night?"

"Yes, Tom, they have. And I did call for help after they attacked me as I was riding my wheel, but I didn't know any one heard me. I began to be afraid no one would ever help me."

"We've been trying to, a long time," said Mr. Damon, "but we couldn't find you. Where did they keep you?"

"Here, part of the time," was Mr. Nestor's answer. "And in other lonely houses. They bound and gagged me when they took me from place to place."

"But what was their object?" asked Tom, concluding it was useless to question the two captives. "Why did they make you a prisoner, Mr. Nestor?"

"Because they took me for you, Tom."

"For me?"

"Yes. The night I called at your house, and found you were not at home, I put back in my pocket a bundle of papers I had brought over to show you. They were plans of a little kitchen appliance a friend of mine had invented, and I wanted to ask your opinion of it."

"These scoundrels must have followed me, or have seen the bundle of papers, and, mistaking me for you, they followed, attacked me in a lonely spot and, bundling me and my wrecked wheel into an auto, carried me off. They first demanded that I gave up the 'plans,' and when I wouldn't they choked off my cries for help and knocked me into unconsciousness. Then they brought me here, and kept me here for several days.

"They soon learned that the plans I had weren't those they wanted, though what they were thin after I couldn't imagine. Only, from what I laser overheard, I knew they mistook me for you and that they were bitterly disappointed in not getting plans of some new airship you were working on. They have kept me a prisoner ever since, and though they offered to let me go if I would keep silent, I refused. I did not think, to secure my own comfort, I should let such men go unpunished if I could bring about their arrest."

"I should say not!" cried Tom.

"Did they treat you brutally, Mr. Nestor?" asked Mr. Damon.

"Not after they found out who I was, by looking through my wallet. Of course they didn't behave very decently, but they weren't actually cruel, except that they bound and gagged me. Oh, but I'm glad you came, Tom! How did it happen?"

Then they told Mr. Nestor their story, and how the test of the new Air Scout had led to his rescue.

"But where are the Secret Service men?" asked Mr. Terrill, when it became evident that none them was on guard at the cabin.

Later it developed that, by following a false clew, the Secret Service men had been drawn miles away from the cabin. And only that Tom and his companions in the silent airship saw the men. Mr. Nestor might not have been rescued for some further time.

His version of what had happened was correct. He had been mistaken for Tom, and the spy with the gold tooth and his accomplice had waylaid Mary's father, under the belief that it was Tom Swift with the plans of the new silent motor. Mr. Nestor had been attacked while riding his wheel in a lonely place, and had been carried off and kept in hiding, a prisoner even after his identity became known.

"Well, this is a good night's work!" exclaimed Tom, when the two rogues had been sent to jail and Mr. Nestor taken to the Bloise farmhouse, to be refreshed before he went home. Word of his rescue was telephoned to Mary and her mother, and it can be imagined how they regarded Tom Swift for his part in the affair.

Little the worse for his experience, save that he was very nervous, Mr. Nestor was taken home. He gave the details of his being waylaid, and told how the men, for many days, were at their wits' ends to keep him concealed when they found what a stir his disappearance had created. The conspirators were well supplied with money, and in the automobile they took their prisoner from one place to another. They had usurped the use of the cabin and had lived there nearly a week in hiding, leaving just before the first visit of Tom and Jackson. The rifled wallet had been dropped by accident.

And it did not take much delving to disclose the fact that, Lydane, "Gold Tooth," as he was called, and his crony, were spies in the pay of the Universal Flying Machine Company. As the men went under several aliases there is no need of giving their names. It is to be doubted if they ever used their real ones—or if they had any.

Of course, there was quite a sensation when Mr. Nestor was found, and a greater one when it became known the part the Universal Flying Machine people had in his disappearance in mistake for Tom. The officials of the company were indicted, and several of the minor ones sent to jail but Gale and Ware escaped by remaining abroad.

It came out that they both knew of the acts of Lydane and his companion in crime, and that the two officials realized the mistake that had been made by their clumsy operatives. It was believed that this knowledge led to the visit of Gale to Tom, the time the latter's suspicions were first aroused. Gale made a clumsy attempt to clear his own skirts of the conspiracy, but in vain, though he did escape his just punishment.

What had happened, in brief, was this. Gale and Ware, unable to secure Tom's services, even by the offer of a large sum of money, had stooped to the sending of spies to his shop, to get possession of information about his silent motor. This was after Gale had, by accident, heard Tom speaking of it to Mr. Damon.

But, thanks to Tom's vigilance, Bower was discovered. The man tripped into the mud hole lost in the muck the plans Bower passed to him. They were never recovered. Then Lydane tried again. He managed, through bribery, to gain access to the hangar where the new silent machine was kept, and, unable to get the silencer apart, tried to file it. In doing so he weakened it so that it burst.

The attempt to waylay Tom, and so get the plans from him, had been tried before this, only a mistake had been made, and Mr. Nestor was caught instead. Finding out their error, Lydane and his companions did not tell the Universal people of their mistake, though Gale and Ware knew the attempt was to be made against Tom Swift.

Later, hearing that the young inventor was still at work on his invention, Gale was much surprised, and paid his queer visit, in an attempt to repudiate the actions of Lydane. At this time it was assumed that Gale and his partner did not know that it was Mr. Nestor who had been kidnapped by mistake or they might have insisted on his release. As it was, Lydane had Mary's father, and was afraid to let him go, though really their prisoner became a white elephant on the hands of the conspirators and kidnappers.

And it was after all this was cleared up, and Mr. Nestor restored to his family and friends, that one day, Tom Swift received another visit from Mr. Terrill, the government agent.

"Well, Mr. Swift," was the genial greeting, "I have come to tell you that the favorable report made by my friends and myself as to the performance of your noiseless motor, has been accepted by the War Department, and I have come to ask what your terms are. For how much will you sell your patent to the United States?"

Tom Swift arose.

"The United States hasn't money enough to buy my patent of a noiseless motor," he said.

"Wha—what!" faltered Mr. Terrill. "Why, I understood—you don't mean—they told me you were rather patriotic, and—"

"I hope I am patriotic!" interrupted Tom with a smile. "And when I say that the United States hasn't money enough to buy my latest invention I mean just that."

"My Air Scout is not for sale!"

"You mean," faltered the government agent. "You say—"

"I mean," went on Tom, "that Silent Sam is for Uncle Sam without one cent of cost! My father and I take great pleasure in presenting such machines as are already manufactured, those in process of making, and the entire patents, and all other rights, to the government for the winning of the war!"

"Oh!" said Mr. Terrill in rather a strange voice. "Oh!"

And that was all he could say for a little while.

But Tom Swift reckoned without a knowledge of a peculiar law which prohibits the United States from accepting gifts totally without compensation, and so, in due season, the young inventor received a check for the sum of one dollar in full payment for his silent motor, and the patent rights thereto. And Tom has that check framed, and hanging over his desk.

And so the silent motor became an accomplished fact and a great success. Those of you who have read of its work against the Boches, and how it helped Uncle Sam to gain the mastery of the sky, need not be reminded of this. By it many surprise attacks were made, and much valuable information was obtained that otherwise could not have been brought in.

One day, after the rogues had been sent to prison for long terms, and Tom had turned over to his government his silent aircraft—except one which he was induced to keep for his own personal use—the young inventor went to call on Mary Nestor. The object of his call, as I believe he stated it, was to see how Mr. Nestor was, but that, of course, was camouflage.

"Would you like to come for a ride, Mary, in the silent airship?" asked Tom, after he had paid his respects to Mr. Nestor and his wife. "We can talk very easily on board Silent Sam without the use of a speaking tube. Come on—we'll go for a moonlight sky ride."

"It sounds enticing," said Mary, with a shy look at Tom. "But wouldn't you just as soon sit on a bench in the garden? It's moonlight there, and we can talk, and—and—"

"I'd just as soon!" said Tom quickly.

And out they went into the beautiful moonlight; and here we will leave them and say good-bye.



THE END

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THE TOM SWIFT SERIES

By VICTOR APPLETON

These spirited tales convey in a realistic way, the wonderful advances in land and sea locomotion. Stories like these are impressed upon the memory and their reading is productive only of good.

TOM SWIFT AND HIS MOTOR CYCLE TOM SWIFT AND HIS MOTOR BOAT TOM SWIFT AND HIS AIRSHIP TOM SWIFT AND HIS SUBMARINE BOAT TOM SWIFT AND HIS ELECTRIC RUNABOUT TOM SWIFT AND HIS WIRELESS MESSAGE TOM SWIFT AMONG THE DIAMOND MAKERS TOM SWIFT IN THE CAVES OF ICE TOM SWIFT AND HIS SKY RACER TOM SWIFT AND HIS ELECTRIC RIFLE TOM SWIFT IN THE CITY OF GOLD TOM SWIFT AND HIS AIR GLIDER TOM SWIFT IN CAPTIVITY TOM SWIFT AND HIS WIZARD CAMERA TOM SWIFT AND HIS GREAT SEARCHLIGHT TOM SWIFT AND HIS GIANT CANNON TOM SWIFT AND HIS PHOTO TELEPHONE TOM SWIFT AND HIS AERIAL WARSHIP TOM SWIFT AND HIS BIG TUNNEL TOM SWIFT IN THE LAND OF WONDERS TOM SWIFT AND HIS WAR TANK TOM SWIFT AND HIS AIR SCOUT TOM SWIFT AND HIS UNDERSEA SEARCH TOM SWIFT AMONG THE FIRE FIGHTERS TOM SWIFT AND HIS ELECTRIC LOCOMOTIVE



SIX LITTLE BUNKERS SERIES

By LAURA LEE HOPE

Author of "The Bobbsey Twins Books,"

"The Bunny Brown Series,"

"The Make-Believe Series," Etc.

Delightful stories for little boys and girls which sprung into immediate popularity. To know the six little Bunkers is to take them at once to your heart, they are so intensely human, so full of fun and cute sayings. Each story has a little plot of its own—one that can be easily followed—and all are written in Miss Hope's most entertaining manner. Clean, wholesome volumes which ought to be on the bookshelf of every child in the land.

SIX LITTLE BUNKERS AT GRANDMA BELL'S SIX LITTLE BUNKERS AT AUNT JO'S SIX LITTLE BUNKERS AT COUSIN TOM'S SIX LITTLE BUNKERS AT GRANDPA FORDS SIX LITTLE BUNKERS AT UNCLE FRED'S SIX LITTLE BUNKERS AT CAPTAIN BEN'S SIX LITTLE BUNKERS AT COWBOY JACK'S



THE MOVING PICTURE BOYS SERIES

THE MOVING PICTURE BOYS THE MOVING PICTURE BOYS IN THE WEST THE MOVING PICTURE BOYS ON THE COAST THE MOVING PICTURE BOYS IN THE JUNGLE THE MOVING PICTURE BOYS IN EARTHQUAKE LAND THE MOVING PICTURE BOYS AND THE FLOOD THE MOVING PICTURE BOYS AT PANAMA THE MOVING PICTURE BOYS UNDER THE SEA THE MOVING PICTURE BOYS ON THE WAR FRONT THE MOTION PICTURE CHUMS SERIES THE MOTION PICTURE CHUMS' FIRST VENTURE THE MOTION PICTURE CHUMS AT SEASIDE PARK THE MOTION PICTURE CHUMS ON BROADWAY THE MOTION PICTURE CHUMS' OUTDOOR EXHIBITION THE MOTION PICTURE CHUMS' NEW IDEA THE MOTION PICTURE CHUMS AT THE FAIR THE MOTION PICTURE CHUMS' WAR SPECTACLE

THE END