The huge man lifted a telephone from an end table adjoining the sofa and set it on the floor alongside Tom.

"Here's a phone. Go ahead and use it, but don't try any funny stuff."

In spite of his headache, Tom's brain was racing. What to do now? He shut his eyes and screwed up his face in an expression of pain, pretending to be still groggy while he stalled for time to figure out his next move.

"How can I get Mirov out of jail?" Tom faltered.

"You figure it out!" the man snarled. "And you'd better get results if you want to stay healthy!"

Through half-slitted eyes, Tom noted the telephone number printed on the dial. Evidently his captor had not thought to remove it from the instrument. A lucky break!

If only, Tom thought, he could devise some way to transmit the number to Ames without arousing his captor's suspicion—the phone's location could then be traced!

What about some sort of double-talk code? For instance, Tom told himself, keep slipping numbers into the conversation in order to transmit the digits of the telephone number. Would Ames catch on?

The number shown was BArwick 3-7156. BA on the dial would be the same as "2, 2."

"Come on! Quit stalling!" the man said threateningly.

"How can I dial with my hands tied?" Tom objected.

"I'll do the dialing, wise guy!"

He lifted the phone from its cradle and extended it to his prisoner. Tom told him the Enterprises number, then asked for Ames's extension as the switchboard operator answered. A moment later the security chief's voice came over the line.

"Ames speaking."

"This is Tom Jr., Harlan." His captor bent close to the receiver as Tom replied, in order to overhear what was being said. "I've been thinking," the young inventor went on, "that it might be smart to have Mirov released."

"Released!" Ames gasped in surprise. "But why, skipper?"

"Well ... er ... as a good-will gesture," Tom said. "I think it might prevent future trouble with the Brungarians, don't you?"

"I do not!" Ames exploded. "The idea sounds crazy!"

"I don't think it's too crazy or too risky," Tom argued. By emphasizing the words, he hoped to impress them on Ames's mind.



Tom's tone of voice and the farfetched nature of what he was saying had already triggered the security chief's suspicions. "Where are you calling from?" Ames asked after a tense pause.

"Shopton," Tom replied. "I just drove in for a haircut." With a chuckle, he added, "Haven't had one in three months. That's a whole week longer than I usually go!"

Would Ames understand that by "week" he meant seven days?... "It's the best I can do," Tom thought.

"Look, skipper, are you sure you want Mirov let out?" Ames said slowly. "I still think it's unwise."

"Consider it an order!" Tom snapped. "This is one thing I insist upon, Harlan. Shouldn't take more than five or six hours, should it, even if he has to wire the Brungarian Embassy to put up bail?"

"It can probably be handled faster than that—if he has any friends around town," Ames said.

Tom took the cue. "Could be," he replied meaningfully.

Tom's captor snatched the phone away and slammed it back on the hook. "All right, smart boy! That's enough!" he growled, glaring at Tom.

Back at Enterprises, Ames hung up thoughtfully. Tom's reply to his last question about Mirov having "friends around town" had convinced Ames that the young inventor was a prisoner, speaking under duress. Moreover, it had seemed as if someone else's breathing was faintly audible in the background, close to the phone.

But what message had Tom tried to convey?

As a routine security-department precaution, Ames's phone was connected to a recorder which automatically taped all calls. Now, while he pondered the problem, Ames pressed a foot-treadle switch to play back the conversation.

Meanwhile, Tom and his captor waited tensely. From time to time the latter glanced at his watch. "Better hope that call does the trick, Swift," he muttered. "It's the only hope you got of leavin' here alive!"

"How will you know if they've turned Mirov loose?" Tom asked. He was wondering if he might persuade his captor to let him make a second call.

"Don't worry. Mirov knows how to contact me."

Half an hour dragged by—then forty minutes. Suddenly the door buzzer rang sharply. The man jerked to attention, obviously startled. He glanced at Tom, then toward the direction of the sound, moistening his lips nervously.

"He must have been expecting just a phone call," Tom decided.

The buzzer shrilled again. This time the man got up from his chair, gagged Tom hastily with a handkerchief, and went to the door.

"Who's there?" he asked loudly.

"Mirov! Let me in, Duffy!" replied an accented voice from outside.

With a look of relief, Duffy started to open the door—then froze as he saw not only Mirov, but two police officers and Ames accompanying him.

"Are you the one who's going to put up bail?" one of the officers demanded.

Duffy floundered, scenting danger but unable to pick up any clue from Mirov's face. "Why—uh—yeah, maybe. How much is it?"

"Ten million! Can you raise it?" Ames snapped sarcastically.

As Duffy gaped in confusion, the officers suddenly flung their weight forward. The door flew open and Duffy was thrown back, almost losing his balance. Beyond, through the small vestibule, Ames caught a glimpse of Tom on the sofa.

"There he is!" Ames shouted.

Moments later, Tom was untied. Mirov and Duffy were handcuffed together.

The young inventor shook hands joyfully with his rescuers. "Nice going, Harlan! Boy, I was sweating icicles here, wondering if you'd be able to decipher all my double talk!"

"You made the numbers clear enough," the security chief said with a grin, "but it took a while to guess what they stood for. And then, of course, we had to trace the address through the telephone company."

Eying the ugly bruise on Tom's forehead, Ames added, "Sure you're all right?"

"Right now I feel swell!" Tom declared, chuckling. He told of his kidnaping, while one of the officers took down the details.

The prisoners were taken off to jail in the police squad car. Tom and Ames, meanwhile, in the security chief's high-powered sedan, drove to the scene of Tom's capture.

They found his sports car badly damaged. The right side was wedged against the utility pole, which was leaning at a crazy angle.

Ames whistled and shook his head. "Boy! You're lucky you got off with just a bruise, Tom!"

"You're telling me," the young inventor agreed ruefully.

After calling a repair garage to send out a wrecker, they drove to the Swifts' home. Mrs. Swift and Sandy, previously unaware of Tom's plight, were horrified to hear what had happened. The sight of Tom's bruise also upset them.

Tom did his best to allay their concern, but finally allowed himself to be hustled up to bed. Dr. Emerson, the Swifts' family physician, was immediately summoned to the house. He pronounced the bruise not serious, but advised that Tom remain quiet, at least for the rest of the day.

Bud came to visit the young inventor that evening, just as Sandy was bringing up a tray. On it was a sizzling T-bone steak.

"Wow! Wish I could have that kind of service," Bud said jokingly. Then he became serious. "I'd sure like to meet that creep who snagged you, Tom. What a fiendish trick! You realize you might have been killed?"

"I realize it, all right," Tom said wryly.

The next morning Tom felt no ill effects from his grim adventure and insisted upon driving to Enterprises. He phoned Admiral Walter, whose report was bleak—the searchers had still gleaned no trace of the buried missile.

Refusing to be discouraged by the news, or lack of news, Tom went to his private laboratory and applied himself once again to the problem of building an "invisible" submarine. But again success eluded him.

At last Tom shook his head in disgust. "May as well get that haircut I started out for yesterday," he decided.

Before leaving, Tom phoned Phyl Newton to thank her for the gift of fruit and nuts she had brought over the previous evening after learning of his dangerous experience. They chatted for a while and wound up by making a date for lunch.

Tom drove back to town in the family car and got a haircut. Then he picked up Phyl at her home and took her to the yacht club. Here they lunched on the terrace overlooking the sparkling blue waters of Lake Carlopa.

The young inventor's spirits were high when he finally returned to his laboratory and buckled down to work.

"I'll lick this problem yet," he muttered. "Those enemies of ours are clever, but if they can produce an undetectable sub, there's no reason why I can't do the same."

Deep in thought, Tom idly fingered a microphone on his workbench.

"In fact," the young inventor mused, "why not go them one better? I'll invent a submarine that's not only invisible to sonar, but equipped to see them!"



CHAPTER XI

SQUARE-DANCE HOAX

Random hunches and circuit diagrams flashed through Tom's brain. "The job will boil down to blotting out sonar waves and piercing the enemy's own 'wave-trap defense,'" the young scientist concluded.

As Tom struggled with the problem, he lost all track of time. A door swung open and high-heeled boots clumped on the floor tiles. Tom looked up and saw the portly, aproned figure of Chow Winkler entering.

"Hi, boss! Can I borrow a radio?" Chow asked. "Kinda like a lil music while I wrassle them pots an' pans in the galley."

"Sure, pardner." Tom pointed toward a portable radio on a shelf nearby.

Chow's leathery face broke into a grin as he picked it up. "One o' them slick lil transistor doodads, eh?"

The cook flicked on the dial knob and the twangy strains of Hawaiian guitar music came throbbing out. A split second later the volume swelled as the same music echoed back to them from the two-room apartment adjoining the lab, where Tom ate and slept when engaged in some round-the-clock experiment.

Chow was startled by the blare. "You got a stereo hookup here, boss?" he inquired.

"Not exactly." Tom explained that the music had merely been picked up by the mike on his workbench, then fed into the adjoining apartment and amplified over a speaker there.

Chow grinned, snapping his fingers to the catchy melody. "Comes out even louder'n it does from the radio!"

"Yes, but the sound quality's not so good," Tom said. "You'd notice the difference with real stereo."

Chow walked out with the portable, crooning contentedly to the music.

Tom frowned, trying to get his train of thought to focus once more on the submarine problem. But for some reason the business with the microphone and the speaker in the next room kept lingering in his mind.

Suddenly Tom exclaimed aloud, "Say! I wonder if that's how the enemy sub blinds our sonar?"

The idea certainly seemed feasible. Suppose the submarine used a great many "microphones"—or receiving transducers—to pick up the sonar pulses beamed out by another craft trying to detect it? These impulses could then be passed on and sent out by speakers on the opposite side of the sub, and relayed along on their underwater path of travel.

Thus the sonar waves would appear to be striking no obstacle—and no echo would return to the sonarscopes on the search craft!

"Jumping jets!" Tom thumped his fist on the workbench in his excitement. "I'll bet that's the answer, all right!" He grinned. "Brand my boot heels, it's partly due to good old Chow!"

He grabbed a pencil and began sketching his idea on paper. It would be necessary to spot the receivers and transmitters all over the hull of the submarine. Diagrams and pages of scribbled computations followed the rough sketches.

An invisible sub—one that sonar pulses would seem to pass right through, as if nothing were there! "Seems so simple now that I have the key!" Tom said to himself elatedly.

Hours ticked by while he analyzed the wave action mathematically, then worked out a typical hookup for one of his jetmarines in a set of precise schematic drawings.

Finally the young inventor dropped his pencil, picked up the telephone, and dialed Bud Barclay.

"Hop over here, fly boy," Tom told his chum. "Something hot on the griddle!"

Bud arrived in a few moments. Tom showed him the drawings and explained his plan for dodging underwater detection. He also related how Chow's remarks about the radio music had sparked the idea.

His chum slapped him on the back. "Good going, Tom!"

"Let's fly right over to Fearing and see how it works on a jetmarine!" Tom proposed enthusiastically.

Bud grinned but made no move. He stood looking at Tom, arms folded and feet wide apart.

"Well, let's go, pal!" Tom urged impatiently, puzzled by Bud's lack of response.

"What about the square dance?"

Tom stopped short, feeling like a punctured balloon. He stared in dismay at his smiling, dark-haired copilot. "Good night! I forgot again!"

With a sigh, Tom added, "You're right, of course. We sure can't let the girls down twice. But at least let's get together all the gear we'll need when we do go to Fearing."

"I guess we'll have time for that," Bud conceded with a sympathetic grin.

Tom assembled a mass of electronic equipment and phoned various Enterprises' departments for other items. Bud helped to collect them, and the boys trucked the paraphernalia out to a hangar to be loaded aboard a Whirling Duck. Then they scootered back to the lab for a quick shower and change.

Twenty minutes later, in sport jackets, checked shirts, and slacks, the two chums hopped into Bud's red convertible. They picked up Sandy and Phyl and drove a little way into the country for dinner at a huge old farmhouse restaurant.

"Well, the evening's off to a good start," Sandy said with a happy laugh as they headed back along the lakeshore road to the yacht club.

"Hope I didn't put away too much fried chicken to sashay properly at the square dance," Bud remarked.

Tom chuckled. "Don't worry, pal. You always untangle those feet of yours when the fiddle strikes up!"

The blazing lights of the yacht club were reflected in the blue-black mirror of the boat basin. Bud parked and they went inside.

"Welcome, buckaroos!" Chow Winkler greeted them with an enthusiastic bellow as they entered the dance room.

The old cowpoke was splendidly dressed in a maroon satin shirt and white whipcord breeches tucked into shiny new boots. But instead of his usual sombrero, a chef's cap was perched on his head.

"Chow! You look marvelous!" Sandy said.

The cook blushed with pleasure. "You gals look purty enough to charm a hoot owl right off'n his perch!" he shot back. Both Phyl and Sandy were wearing gay calico dresses that had full swirling skirts.

The room was decked out with colored bunting and twisted crepe-paper streamers. And at one end of the dance room, Chow had rigged up a model of a Western chuck wagon.

"Real atmosphere!" Tom said admiringly. "Chow, you've done us proud!"

"Thanks, boss." The cook, who had asked especially to take charge of the decorations, glowed at the praise. Then he became serious. "But what's keepin' that dad-blamed fiddler?"

The guests soon began to stream in, but half an hour went by, and Lester Morris and his fellow musicians had not arrived.

"I'd better phone his house," Tom decided worriedly.

Mrs. Morris answered. She seemed surprised at Tom's call. "Why, my husband's playing at a party over in Carterton this evening," she said. "Are you sure you engaged him for tonight?"

"I'm positive," Tom replied.

"Just a moment, please. I'll look in his date book to see if there's been a mistake."

A minute later her voice came over the line again. "I'm terribly sorry, Mr. Swift, but your name isn't listed anywhere on Lester's schedule."

The others saw from Tom's face as he hung up that something was wrong.

"What gives?" Bud asked anxiously.

"No music for one thing." Tom reported what Mrs. Morris had told him.

"But you hired the guy!" Bud protested. "And Sandy and I talked to his agent!"

Tom was already piecing together the mystery. He shook his head thoughtfully. "I'm sure now the whole deal was a hoax, Bud," he declared. "Both the first call that supposedly came from Lester Morris, and the second one asking me to come here and talk things over."

By not responding to the second call in person, Tom went on, he had probably saved himself from being waylaid or kidnaped by his enemies.

"Thank goodness!" Sandy exclaimed. "Still, that creepy Len Unger was trying to get information from us."

"But how did your enemy know about the dance, Tom?" Phyl Newton put in.

Sandy snapped her fingers. "I know! I'll bet it was when we went shopping for our dresses, Phyl, right after the boys invited us! The department store was full of people—almost anyone might have heard us discussing the dance!"

"Especially if he was already trailing you to pick up bits of useful information," Tom agreed.

Bud whipped out a handkerchief and mopped his face nervously. "The question is what do we do now, chums? A roomful of guests and no music!"

"Relax, pardners!" Chow broke in cheerfully. "Just keep things goin' for a spell, an' I'll fix things up pronto!"

Doffing his chef's cap, Chow hustled out to his parked jeep and took off with a roar. Mystified but hopeful, Tom, Bud, and Phyl did their best to entertain the guests. Sandy had rushed to the telephone. In twenty minutes Chow came rushing back.

"Hey! He has a fiddle!" Bud exclaimed.

Mounting the platform, the stout cowpoke raised his hands and shouted for attention.

"Ladies an' gents, we'll start off with that good old dance known as the Texas Star!"

As everyone took his place, Chow tuned up hastily. Then he tucked the fiddle under his chin, stomped out the rhythm, and launched into a lively rendition of "Turkey in the Straw" while he called out the accompaniment:

"Gals to the middle, then back so far! Gents step up for a clockwise star! Now shift hands and twirl t'other way, We'll keep on dancin' till the break o' day...."

The dance number finally ended to thunderous applause. Chow, puffing and red-faced but wreathed in smiles, was soon ready for another. Half an hour later, a dance band of high school boys, hastily summoned by Sandy, arrived to spell the Texan.

The irrepressible chef, however, continued to call out most of the numbers and proved to be the hero of the evening. He gained even more acclaim for his delicious French fried potatoes and "steerburgers" served during the pause for refreshments.

"Oh, Chow! What would we ever do without you?" Sandy said, and the cook beamed.

Suddenly, in the midst of the lively chatter and laughter, the dance floor was plunged into total darkness!

Phyl clung fearfully to her escort. "Tom!" she gasped. "This is another trick of your enemy's to harm you!"



CHAPTER XII

DETECTION TEST

"Don't worry, Phyl. It may be only a blown fuse," Tom tried to assure the fearful girl.

But Tom was worried himself. Not only might he be in danger, but it could involve his friends!

Nevertheless, he raised his voice above the excited babble. "Please be calm, everyone! We'll have the lights on again in a jiffy!"

Taking Phyl by the hand, Tom groped his way toward the main door.

"Let's check the switch," he murmured, and ran his hand over the wall near the door. He located the metal plate and flipped the switch.

The lights went on! Good-natured cheers arose. Bud, grinning but puzzled, left Sandy's side long enough to come over and speak to Tom.

"What happened?"

"I guess some practical joker clicked off the switch."

Bud suddenly caught sight of a stout youth in a plaid shirt and blue jeans, who was standing in a nearby corner. He was shaking all over with half-stifled merriment.

"There's the wise guy! Rock Harriman!"

Rock, an all-star tackle on the Shopton High football team, was well known for his pranks and practical jokes. Bud rushed over.

"Okay! Confess!" the husky young flier roared in a jokingly ferocious tone.

"Don't get sore!" Rock gasped between chuckles. "I couldn't resist. Boy, did you hear everyone squeal when the lights went out?"

Tom grinned in relief. "How about another dance, Phyl?"

As the music struck up again, he squeezed Phyl's hand. "I sure appreciate your concern, even if I didn't rate it."

Phyl blushed as she returned the squeeze. "You rate with me," she confided shyly.

The festivities finally ended after a thoroughly enjoyable evening. Both Sandy and Phyl declared to their dates that it more than made up for the forgotten beach party.

"But let's not wait too long for the next date," Sandy warned playfully.

"Okay, that's a deal," Bud promised.

The next morning at the plant Tom called on Harlan Ames. He told of the sinister hoax by the caller who had passed himself off as Lester Morris. The security chief promised to investigate.

"I'll tip off the police about Len Unger," Ames added. "If they can find him, we may be able to crack this case wide open."

Tom telephoned Bud, Hank Sterling, and Arv Hanson to meet him at the helijet hangar. The four took off in one of the Swifts' Whirling Ducks, which was standing by loaded and ready. Soon they landed on Fearing Island, where Tom would try out his antidetection invention.

"What'll we use for a test sub, skipper?" Hank asked as they drove toward the docks.

"A jetmarine," Tom replied.

A truck with engineers and technicians was following the jeep. It carried the equipment which Tom and Bud had assembled the previous day.

When they arrived at the docks, Tom gathered the men in a loading shed. He showed them his drawings and explained how his "sonar-blinding" setup would operate.

"Don't let the diagrams fool you. The basic idea is very simple. We absorb all sonar impulses that hit the ship and transmit them out the opposite side of the hull, instead of letting a ping bounce back and show up on the sonarscope of any hostile sub on the lookout for us."

Most of the job, he went on, would be tedious detail work. It would consist of attaching hundreds of mikes and speakers all over the hull to pick up and transmit the sonar pulses. The mikes would be receiving transducers and the speakers would be transmitting transducers.

"The leads from them," Tom ended, "will be centralized in a single electronic control unit inside the ship. I'll handle that part of it."

"Great idea, Tom!" Arv Hanson said admiringly.

"But what a job it'll be rigging those transducers," put in one of the technicians.

Tom nodded wryly. "You're right, Danny. If this experiment works out, though, I think I can lick that problem on future installations."

The young inventor explained that he hoped to find a way to mold the transducers into a continuous plastic sheet. This could be applied to the hull of a submarine in a single operation.

"But this time we'll have to do it the hard way," Tom added with an apologetic grin.

A jetmarine was hoisted into drydock and the work crew swarmed over it, rigging the transducers. Would his experiment succeed? Tom wondered. Hopefully, he set to work assembling the electronic control unit.

Bud helped the men on the hull for a while, then descended through the hatch to see how Tom was progressing.



"I'd go gaga trying to keep track of those circuits," Bud said, as he watched Tom installing the delicate transistors and other components with an electric soldering gun.

The young inventor grinned. "It'll be simple enough when the control unit's all put together," he replied. "Just a single on-off switch and one test circuit."

By noon, after working at a frenzied pace, the job was done. Tom thanked each one of the men personally. Then everyone went to eat lunch.

After the meal, Hank Sterling asked, "How about a detection test to see how she works?"

"Coming right up," Tom said. "Want to skipper the jetmarine, Bud?"

"Sure do!"

"Okay. Pick out a couple of men for a crew and take her down." Tom produced a hydrographic chart of the waters around Fearing and marked out a test area. "Cruise around there for an hour and we'll try to spot you in the Sea Hound."

"Hide and seek, eh?" Bud grinned and snapped a salute, then left to supervise the relaunching of the jetmarine.

For his crew, Bud chose Mel Flagler and another man. Mel was an experienced jetmariner who had gone on the Swift expedition to Aurum City, the underwater ruins of a lost civilization. Here Tom had used his spectromarine selector to restore the ancient buildings.

Tom, Hank, and Arv went back to the airfield and soon took off in the diving seacopter. Landing on the water, they submerged and began the undersea detection test.

Tom manned the sonarscope personally, eager to conduct as careful a search as possible.

"Getting any blips, skipper?" Hank called out from his post at the Sea Hound's controls.

"Not a ping, Hank. The system seems to be working out even better than I'd hoped."

Tom felt a glow of satisfaction. He explained, however, that the jetmarine's transparent nose pane—which had to be left unprotected for the pilot's visibility—offered one vulnerable spot to sonar detection.

"But a little smart maneuvering can cover up that angle," Tom added. "Try the hydrophones, Arv, and see if you can hear 'em."

The chief modelmaker slipped on the earphones and listened intently. For another ten or fifteen minutes they probed about with no sound trace of the "invisible" jetmarine.

But presently Arv snapped his fingers to catch Tom's attention. "Got her, skipper!"

Tom took over the hydrophones. Sure enough, his ears could make out the faint hum of the jetmarine's atomic turbines. Tom directed Hank toward the sound, then ordered him to switch on the Sea Hound's powerful search beam.

The light cut a path of radiance through the murky dark-green waters. Dead ahead, the jetmarine could be seen gliding across their field of view.

"Your system blinded our sonar okay, skipper," Hank commented, "but this proves she could still be spotted by enemy listening devices."

Tom refused to be discouraged. He ordered Hank to return to base and wait for Bud. Meanwhile, the young inventor applied himself to the problem of how to mask the sub's noise.

"How about it, pal?" Bud asked, when he reported aboard the seacopter a while later.

Tom explained the results of the test and the need for an added safeguard against hydrophone detection. "Think I see a simple way out, though," he added with a pleased chuckle.

"Natch! With a brain like yours, it's a cinch," Bud quipped. "Explain, professor."

"Well, we can never do away with the noise of a sub's propulsion machinery," Tom began. "That goes without saying. So we'll have to camouflage it—lose it in the underwater jungle noises, so to speak."

Bud scratched his head. "How do we do that?"

"By amplifying the natural undersea sounds all about it," Tom explained. "Fish and all forms of underwater life make a background noise over the hydrophones, you know."

As Bud nodded, Tom went on, "So we simply step up the volume till the sub's own noise gets drowned out or 'wasted' in all the racket."

This could be done, he concluded, with fairly simple amplifying equipment. Bud, Hank, and Arv were jubilant at the idea.

"Nice going," Bud said. "How soon can we give it a try?"

"Soon as I can rig up the amplifier," Tom promised.

In less than two hours they were ready to submerge again. Zimby Cox joined the crew. Bud suggested taking along hydrolungs in case of any need for tinkering with the transducers or amplifying equipment.

This time, the jetmarine scored perfectly on the test, successfully eluding all the Sea Hound's efforts to detect it. Tom returned happily to base, feeling that the antidetection problem was now solved. The jetmarine, however, failed to appear.

"That's funny. The test was over at four-fifteen," Tom murmured.

"Maybe Bud surfaced out at sea somewhere," Arv Hanson suggested.

Repeated radio calls brought no response. Tom, now seriously worried, took the seacopter down again for another search, hoping that Bud would have switched off the antidetection gear by this time. But neither sonarscope nor listening devices revealed the slightest clue.

Tom, Hank, and Arv exchanged fearful glances. Had the jetmarine foundered on the ocean bottom—perhaps fouled somehow by Tom's new invention? Or had Bud and his crew fallen victim to the enemy?



CHAPTER XIII

ENEMY FROGMEN

At the end of the test period, Bud had prepared to bring the jetmarine to the surface. But just as he was about to blow the ballast tanks, Mel Flagler sang out a warning from the sonarscope.

"Whoa! Hold it, skipper! I think we have company on the starboard beam!"

Bud jerked his head around in surprise. "You mean the Sea Hound?"

"No, she surfaced," Mel reported. "Can't make this out yet, but it could be another sub."

Bud turned the controls over to Zimby Cox. Then he rushed to the scope and examined the blip. "Seems to be moving away from us on a westerly course. It's about two miles from here."

He donned the hydrophone earset and listened. "It's no seacopter, nor a jetmarine either," he announced presently.

"A Navy sub, maybe?" suggested Zimby.

Bud shrugged. "Let's find out." He ordered a change of course, hard to the right, and gunned the jets to bring the jetmarine directly on the mystery object's trail.

"It's a sub, all right," he said a short time later, listening again over the hydrophones.

"Pretty close to Fearing Island, isn't it?" put in Mel Flagler. "That's a government-restricted area."

Bud nodded grimly. "But staying just out of sonar range from the base."

The jetmarine closed steadily on its quarry. In a few minutes they were able to make it out dimly through the cabin window, dead ahead.

"That's sure no U.S. Navy sub that I know of," Bud said. "Probably an enemy snooper."

"What if they spot us?" Zimby asked.

Bud chuckled. "That's the beauty of it, pal! Don't forget. With this new antidetection gear we're invisible to them. At least as long as they don't run into us or we into them," he added.

"Or unless they have superdetection equipment we don't know about," cautioned Mel Flagler.

As they talked, the unidentified submarine was bearing steadily toward the mainland. Fathometer soundings showed it was on a steep upward slope of the continental shelf.

Presently a foaming gush of bubbles showed that the sub ahead was blowing its tanks. The jetmarine followed as it surfaced and Bud hastily manned the periscope.

"What're they up to?" Mel asked tensely.

"Don't know yet, but the hatch is opening," Bud reported. Suddenly he gave an excited gasp. "Jumpin' jets! They're sending out a couple of frogmen!"

Bud's companions were electrified by the news.

"Spies!" Zimby exclaimed.

"What do we do now?" piped up Mack Avery, the third man in Bud's crew. "Hadn't we better radio the Coast Guard and the FBI?"

Bud wrenched away from the eyepiece. "I have another idea! Any of you fellows game to go with me and capture those spies?"

All three of his companions volunteered eagerly. Bud chose Mel Flagler, then took another sight through the periscope.

"The sub's submerging again," he reported. "That'll give us a clear field. Zimby, you and Mack keep an eye on that baby while we're gone, and be plenty careful she doesn't spot you!"

"Roger! And take this roll of wire to tie up your prisoners."

Hastily Bud and Mel changed into swimming trunks and donned hydrolungs. They went out through the air lock, plunged into the bracing salt water, and switched on their ion-drive units.

"Can you see 'em?" Mel asked over his mike.

"Not yet. Let's speed up before we lose 'em completely!"

Both pushed their ion drives to capacity, scanning the water ahead in all directions.

"There they are!" Bud exclaimed presently. He pointed to two tiny figures, barely visible in the distance.

"Wow! They're sure not wasting any time!" Mel muttered. "Let's step on it, Bud! They'll be ashore in a minute!"

A darting school of sea bass screened the figures briefly from view. As the fish flickered past, Mel and Bud saw the frogmen breast-stroke up toward the surface and break water.

Bud and Mel followed. Ahead lay a barren stretch of beach, humped with sand dunes. It was skirted beyond by a thick fringe of trees.

"They certainly picked a perfect spot for a sneak landing!" Bud thought. The beach seemed totally deserted, with no sign of human habitation.

By this time, the frogmen were scrambling ashore. Within moments, Bud and Mel were on their heels. The raiders whirled in dismay as they caught the sound of footsteps rushing up behind them through the sand.

Bud and Mel hurled themselves forward, each dropping a man with a flying tackle. All four went down in a struggling, kicking tangle of arms and legs.

The battle was rough but short. Bud and Mel had the advantage of surprise, and soon pommeled and grappled their foes into submission.

Bud, astride his opponent's chest with knees pinning the man's arms, unlooped from his belt the wire he had brought.

"Here! Take some of this and wire your man's wrists together!" Bud told Mel.

When the frogmen were safely bound, Bud and Mel allowed them to stand up. Neither captive tried to escape.

"Now, my sneaky friends, talk!" Bud snapped. "What kind of a sightseeing trip did you plan?"

The frogmen's jaws remained tightly clamped. Both looked flushed and sullen as they faced their captors.

"Got their lips zipped, I guess," Mel said disgustedly.

Bud decided to try another tack. "Doesn't matter," he said carelessly. "We know they're pals of the Mirovs."

Both men started as if they had been stung. Bud followed up quickly, hoping to prod them into some unguarded remark.

"Just as we thought!" he snarled. "A couple of low-down Brungarian rebels! And up to their usual amateurish spy stunts!"

The raiders' eyes blazed, but they maintained silence. Both, however, kept darting looks of keen interest at the Americans' hydrolung gear.

Just as Bud was wondering how he could get the prisoners to the nearest police headquarters, a jeep came bouncing into view across the sand.

"Hey! Police!" Mel exclaimed with a happy grin.

"We're in luck," Bud said. "They can take these creeps off our hands."

The jeep braked to a halt a few yards away, and two uniformed officers hopped out.

"What's going on here?" said one, who was wearing a sergeant's stripes. The jeep had the words BEACH PATROL stenciled on it in white paint.

"We just nailed these two Brungarian frogmen," Bud explained. "A sub put them ashore—probably as spies or saboteurs. They won't talk to us, but maybe you can pump them at headquarters."

The startled sergeant turned a cold eye on the two prisoners. "Got anything to say for yourselves?" When neither answered, he unholstered his revolver and covered them. "Better take off those wires and put bracelets on them, Mike," he told his fellow officer.

The frogmen were handcuffed with cool efficiency and bundled into the jeep. Meanwhile, the sergeant turned back to Bud and Mel.

"You fellows come along too," he ordered.

"But we haven't got time," Bud protested. "Our own sub's waiting right offshore and we want to tail the sub that brought those guys here! We're from the Swift rocket base."

"Any identification?" the sergeant asked.

"How could we have in this getup?" Mel retorted.

"That's what I thought. So get moving," the sergeant barked.

Reluctantly, Bud and Mel hopped onto the running board and clung to the bouncing jeep as it sped to the nearby town of Sandbank. At headquarters they were questioned by the local police chief.

"If you'll call Swift Enterprises at Shopton, sir, Mr. Swift—or Harlan Ames of the plant security department—will vouch for us," Bud said.

The chief picked up the telephone and soon had Mr. Swift on the line. After speaking to him briefly, he passed the phone to Bud so the scientist could identify his voice.

"That's Bud Barclay, all right. He's one of our most trusted employees," Mr. Swift told the chief after hearing Bud's story.

The officer promised to release Mel and Bud at once. Before doing so, however, he took them into the adjoining office where the two frogmen were being questioned.

"Any luck?" the chief asked the sergeant.

Sergeant Gryce shook his head in disgust. "Not much. They did admit they came in a sub, but they claim it didn't wait to pick them up."

The police chief shot a few questions of his own at the men, but they answered either in curt monosyllables or not at all.

"Look, sir," Bud put in, "if they're telling the truth about their sub not waiting, our jetmarine may have chased it. That means Mel and I are stranded here. Could you have your men wait for us on the beach till we find out?"

"Gladly," the chief replied. "You two have done a fine day's work."

After the prisoners had been locked up to be handed over to the FBI, the two Beach Patrol officers drove Bud and Mel back to the area where they had landed. Just as the jeep turned down the dirt road leading to the shore, Bud's keen eyes spotted a lurking figure in the distance.

"Stop, please!" Bud said, tapping the driver on the shoulder.

As the jeep halted, Bud pointed toward the beach. A man was crouching behind a sand dune, with a large fish basket beside him. The sergeant, puzzled, took out a pair of binoculars to study the situation. Fortunately, the jeep was still screened by trees, and the crouching man evidently did not realize he had been seen.

"What's in the basket?" Bud asked. "Could it be clothes?"

"Sure looks like it," the sergeant said, passing over the binoculars.

After a brief look, Bud explained the hunch that had occurred to him. "I'll bet that guy's waiting with clothes for the frogmen. He probably got here late and doesn't realize they've been nabbed!"

"Well, he'll soon find out," the police driver said grimly. He was about to start up the jeep when Bud stopped him again.

"Wait! You have no proof that's what he's here for," Bud pointed out.

The pilot suggested that the police keep out of sight while he and Mel approached the man in their swimming gear. "If that stranger takes the bait, we'll really have the goods on him!" Bud concluded.

"Smart idea, son," the sergeant said with a dry chuckle. "Go to it!"

Bud and Mel circled widely through the trees, took a quick dip in the water, then approached along the beach as if they had just landed and were searching for someone.

To their delight, the man rose from behind the sand dune and hailed them. Bud and Mel hurried over to him.

"You have clothes for us?" Bud asked. "We just came ashore from the sub!"

"Yeah, right here," the man said in English with no trace of an accent. "Thought I'd missed you."

"Thanks, pal—that's all we want to know!"

The man gaped in comic dismay as Bud pounced on him and pinned him to the ground. Moments later, the two police officers rushed up and handcuffed him.



"Hey! What's the big idea?" the man stammered. "I ain't done nothing. Just got a phone call this morning, offering me fifty bucks to bring two sets of clothes down to the beach at five o'clock for a couple of divers."

"Tell that to the FBI!" snapped the sergeant.

When the officers had departed with their new prisoner, Bud and Mel, both grinning, dived into the surf and headed out to sea.

In a few minutes they were sure they were at the right spot to meet the jetmarine. But it was gone!



CHAPTER XIV

A PROPAGANDA BLITZ

As the Sea Hound returned to Fearing Island from its search for Bud's jetmarine, Tom was beside himself with worry. Had his experiment cost the lives of his best friend and the other crewmen aboard?

"I'll never forgive myself if anything's happened to them!" Tom muttered bleakly.

Hank Sterling squeezed the young inventor's arm. "You know Bud's high spirits, skipper," he said. "He may have taken off on some crazy lark."

"Sure! A whale hunt, maybe!" Arv Hanson wisecracked, trying to lighten the gloom.

Tom forced a grin, but he remained heavy-hearted as they neared the base. His only hope now was that a radio message from the jetmarine might have been picked up while they were gone.

As soon as the seacopter was moored, Tom leaped ashore. The crewmen on the docks had no news to report, so Tom piled into a jeep with Arv and sped off to the Fearing communications center. Hank remained aboard the Sea Hound to secure all gear.

Churning along the graveled road, Tom and Arv passed the launching area. Huge, needle-nosed cargo rockets and the mighty spaceship Titan loomed against the sky. Tom's moon-voyaging Challenger and his more recent space craft the Cosmic Sailer were also based there.

"Going to alert the Navy for a search?" Arv inquired as they reached the communications building.

Tom nodded and braked the jeep to a screeching halt. "Coast Guard too. They can pass the word to commercial shipping to be on the lookout."

A telephone rang as he hurried into the office.

"For you," the clerk said, looking up at Tom. "Nice timing!"

Tom grabbed the phone. His face widened into a grin. "Bud! You seagoing jet stream! What happened?"

Arv grinned, too, in relief.

"Your antidetection gear worked so well we vanished right out of the ocean!" Bud replied with a chuckle. Turning serious, he reported how his jetmarine had trailed the mysterious intruder and how he and Mel had captured the two Brungarian frogmen and their shore contact.

"Nice going, pal!" Tom exclaimed.

"But here's the catch," Bud went on. "When we took off again in our hydrolungs to go back aboard ship, the jetmarine was gone!"

"Maybe she's trailing the enemy sub," Tom conjectured.

"That's what I'm hoping," Bud said uneasily. "Trouble is, our subs aren't armed, and who knows about that Brungarian job? The way they sling missiles around, anything could happen if she spots the jetmarine."

Tom frowned. "I'll organize a search right away. Where are you calling from?"

"Police headquarters at Sandbank."

"Okay. Take it easy, and I'll send a whirlybird to pick you up," Tom promised.

"And don't forget some clothes," Bud added with a chuckle. "Mel and I are getting chilly."

"Right!" Tom hung up and gave Arv Hanson a quick briefing.

Then he phoned the base airfield to dispatch a helicopter. He also contacted the nearest Coast Guard station and put through a long-distance call to Navy Headquarters in Washington to request help in searching for the jetmarine. Finally he and Arv headed back to the submarine docks in the jeep.

A flurry of activity followed as Tom detailed ships for the search and rounded up crews. He was interrupted by a phone call in the loading shed. It was the control-tower operator.

"One of our drone planes has spotted a sub approaching, skipper," the operator reported.

"What bearing?" Tom demanded excitedly.

"One-seven-six." Tom was about to hang up and grab a pair of binoculars when the operator added hastily, "Wait! It's responding to our radio challenge!... That's ours, all right!"

Tom dashed out of the shed and scanned the sea to the southward. Sure enough, a jetmarine had surfaced and was speeding toward the sub docks. Minutes later, Tom was shaking hands warmly with Zimby Cox and Mack Avery.

"Is Bud okay?" was Zimby's first question.

"Right! I just heard from him," Tom replied. "He and Mel captured those enemy frogmen and a copter's on the way to pick them up. What happened to you fellows?"

Zimby confirmed Bud's guess that they had taken off in pursuit of the enemy craft.

"We figured Bud and Mel could make out on their own," Zimby explained. "And we thought the sub's course or actions might tip us off to its nationality. Also, if it tried any sabotage or mine-planting, we could radio the Navy."

Instead, Cox went on, the mysterious craft had proceeded to a point about ten miles offshore where it rendezvoused with another submarine.

"And get this, skipper!" Mack Avery put in. "The other sub was undetectable! We were close enough to get a peek at it, but we couldn't ping it on the sonarscope."

"That figures," Tom said grimly. "Those frogmen were apparently Brungarians."

Zimby Cox related that a man had transferred from the undetectable submarine to the one they had been following. The first sub had then headed out to sea, as if to cross the ocean back to its home base. The other had departed on a course toward the South Atlantic.

"Probably back to the lost missile area. At least that's the way we figured it," Zimby added.

"And neither sub spotted you?" Tom questioned.

Zimby grinned wryly. "We might not be here if they had detected us. But I'm pretty sure they didn't. Anyhow, they gave no sign."

Tom was doubly elated at the news. His antidetection gear had evidently worked perfectly in a showdown test with the enemy, even at close range. Moreover, if the second sub was returning to the South Atlantic, it seemed likely that the enemy, too, had not yet located the precious missile with its data from Jupiter.

"You guys rate Navy medals," Tom told Zimby and Mack jubilantly. "Come on back to Shopton with me and I'll buy you the juiciest steaks in town!"

Before leaving the base, Tom called the Coast Guard and the Navy to cancel his search request. He also telephoned a full report on the enemy submarines to Admiral Walter.

After hanging up, Tom decided on another move. "Our antidetection gear seems to have panned out pretty well," he told Hank. "I think we should make use of it right away. By sending that jetmarine to the South Atlantic, we might get a line on enemy activities down there."

Hank was in favor of the idea. He volunteered to prepare the jetmarine for a cruise and take off from Fearing that very night.

"Thanks," Tom said with a parting handshake. "Keep us posted if you learn anything."

Meanwhile, Bud and Mel Flagler had arrived at the base by helicopter. They and their two shipmates flew back to the mainland with Tom and Arv for a celebration dinner in town.

The next morning found the young inventor hard at work in his private laboratory. He was tapping his head with his slide rule and frowning at a blackboard scrawled with equations when Bud dropped in for a visit.

"What now, inventor boy?" his copilot asked. "Don't you ever give that brain of yours a rest?"

"Oh, hi, Bud!" Tom looked around absent-mindedly. "I'm just trying to figure out a way to crack the Brungarians' antisonar system."

"Good night!" Bud sank down on a lab stool. "You've come up with a way to make our own subs undetectable. Isn't that enough?"

Tom shook his head. "Not if we want to keep track of those sneaks. And I think I see a way to do it."

"How?"

"So far, I have been thinking about refining our own search sonar." Tom explained that the new system he had in mind would send out a complex pulse—that is, an underwater sound wave with many harmonics instead of a single tone, sharp-peaked sound impulse.

"This will make it less likely that their antidetection gear will absorb all of it," Tom went on. "What's not absorbed will return as an echo. I'm also going to modify our receivers. But I've still not worked that out."

Bud nodded, his forehead puckered in a look of concentration. "So—?"

"So our sonar picks up all that hash, and by means of a computer setup filters out the sub's real echo from the shadow reflections."

"Hey! Sounds pretty cute," Bud said.

Tom broke into a dry chuckle. "Right—if I can do it." After that job, Tom added, he hoped to adapt his own antidetection methods to make hydrolung wearers safe from underwater detection. "And if the Jupiter prober hasn't been found by that time, Bud, I'm going to request the Navy to let us take over the search alone."

Bud gave a whistle of excitement at the possibility of new undersea adventures ahead. "Count me in, pal!"

The two boys broke off their conversation a short time later and went back to the Administration Building for lunch with Tom's father.

Mr. Swift greeted them with a smile as they entered the big double office. "Glad you could join me, boys! Chow's laid out quite a feast for us today."

Three places had been set at the conference table, and an appetizing repast of sizzling ham and sweet potatoes waited in covered dishes on a lunch cart nearby.

"Mmm!" Bud inhaled the aroma. "Good chow from good old Chow!"

Tom switched on the videophone screen to a private channel to catch the noon news while they ate. The newscaster wore a look of excitement as he spoke without pausing for the usual commercial.

"The Brungarian government has just scored a propaganda bombshell!" he reported. "In a news announcement released less than half an hour ago, they stated that their Navy has perfected an undetectable submarine!"

The Swifts and Bud froze, openmouthed, at the newscaster's words.

"No need to tell you what this could mean to American security," he went on. "If enemy subs slipped through our continental defenses, their missiles could devastate the United States with scarcely an instant's warning! The whole country's been rocked by the announcement. An official comment by our Defense Department is expected at any moment."

"Sufferin' satellites!" Bud gulped.

Mr. Swift nodded. "It's a great propaganda stroke. But I wonder why they've chosen to reveal their secret at this time."

Tom said thoughtfully, "Dad, do you suppose they've realized the fact that we know about their antisonar gear?"

"Could be, son. They may figure that since the secret is out already, they may as well play it up for all it's worth." The elder scientist paused and frowned. "Or it might be intended to force our hand."

"You mean in hopes of getting us to reveal whether or not we have an antidetection system ourselves?" As his father nodded, Tom scowled. "If so, that sub yesterday may have been observing our tests."

The telephone rang and Tom leaped to answer it. The caller was Dan Perkins of the Shopton Evening Bulletin.

"You can guess why I'm calling, Tom," the editor said. "How about a statement from you Swifts on this Brungarian sub story?"

"We found it very interesting," Tom said politely but noncommittally. Parrying further questions, he hung up as soon as possible.

Mr. Swift approved Tom's policy of silence. Almost immediately the phone began ringing again with a succession of calls from other newspapers and wire services. Tom dashed off a brief, general statement and instructed Miss Trent to give it to all further callers.

"Maybe this is a good time to make a private announcement to you fellows," Mr. Swift said to the two boys, his eyes twinkling. "Do you recall my telling you that Doc Simpson had isolated an unknown vitamin from the space plants? Well, we've now discovered that this vitamin can condition the human body to stay under water indefinitely. Doc is putting some up in capsule form."

Both Tom and Bud gave whoops of glee at this news.

"Dad, you've helped overcome one of the big problems in our search for the lost missile!" Tom exclaimed.



CHAPTER XV

MOUNTAIN HIKE

"After adequate doses of your space vitamin, Dad, a skin diver could tackle almost any undersea job in my hydrolung!" Tom exclaimed. "He wouldn't be subjected to any antiosmosis troubles with his body tissues."

His father nodded. "For the first time, man might become a truly marine creature!"

"Wow! Think of it!" Bud gasped excitedly. "With Tom's hydrolung and a knife to hunt his own food, he could practically live in the sea!"

"That's no farfetched dream, Bud." Tom's steel-blue eyes flashed at the thought of new fields of scientific conquest. "This discovery of Dad's and Doc Simpson's opens up some really amazing possibilities."

Most important at the moment, the vitamin would be a great boon in carrying out search and digging operations for the Jupiter prober. With fresh enthusiasm, Tom returned to his laboratory to work on the new sonar gear. In his own mind, he had already named it a "quality analyzer sonar," since that exactly described the way it would function.

"Hmm, let's see," Tom mused as he settled down at his workbench, pencil in hand. "Besides a regular sonarscope, I'll need at least three units for the gear."

First, he would need an oscillator to produce the complex pulse. Next, of course, an oscilloscope to check the pulse as it was beamed out. Last—but highly important—a correlation calculator.

This latter unit would compare the original pulse with the returning echoes. If an echo had a high enough "standard of acceptance"—that is, if its quality was very near the original pulse, it would show up on the screen in the normal way. If the echo came back blurred, or if "shadow echoes" showed up, these would be separated and appear on the screen colored red.

"Whew!" Tom sighed as he realized the complicated job of circuit design that lay ahead. "This sure is going to burn some midnight oil!"

The young inventor worked all afternoon at a furious pace, breaking off toward dinnertime to telephone his mother that he would be staying overnight at the lab. After a hasty meal, he resumed his layout job at the drawing board and by midnight had finished designing his quality analyzer sonar.

Whipping off his eyeshade, Tom went into the apartment next door and stretched out to snatch a few hours' sleep. But as usual when in the midst of an exciting new project, he was too keyed up to rest for long.

Before daylight, Tom was back at his workbench ready to begin assembling the units of his new sonar gear. Later he phoned Chow but scarcely paused to eat when the cook arrived with his order.

"Brand my solar stovepipe!" Chow scolded. "Take time to eat your vittles properly, boss!"

"Hmm?... Oh, sure." Tom looked up and grinned.

The stout old Texan stomped out, shaking his head.

As the morning wore on, the pace at which Tom had been working began to tell on the young inventor. His head nodded again and again. Gradually he fell forward into an exhausted doze.

The next thing Tom knew, he was sailing through the air, high above Swift Enterprises. Lake Carlopa was a tiny blue puddle below, and the town of Shopton a mere cluster of toy buildings in the distance.

"Good grief!" Tom exclaimed with a gulp. "What's keeping me up?"

He was floating freely, without the support of any aircraft—or even one of his amazing force-ray repelatrons!

The discovery triggered off disaster. Like a character in a movie cartoon, now that he knew he had nothing to support him, Tom instantly went plunging downward—down, down, straight into the lake!

Splash!

Tom gasped and shuddered and shook his head like a drenched terrier.

Another splash! As Tom brought his eyes into focus, he realized he was back at his workbench in the laboratory. Chow was standing in front of him, holding a half-empty pail of water, ready to splash him again!

"Hey! Cut it out!" Tom cried out, jerking bolt upright. Then, as he saw the disturbed look on Chow's face, Tom burst out laughing. "Okay. Relax, old-timer! Guess I was dreaming."

"Brand my snake oil!" Chow said. "You looked so pale an' pasty, you had me plumb scared, Tom! I couldn't wake you nohow!" Worriedly the cook added, "What you need is a good beefsteak and some sunshine. You been under water too long."

"In more ways than one!" Tom chuckled as he grabbed a towel and dried himself off.

The beefsteak, with crisp golden-brown French fried potatoes, was already at hand on Chow's lunch cart. Tom ate with a hearty appetite and the stout chef went off, secretly plotting to arrange the second half of his prescription.

When he reached the galley, Chow plucked the wall phone off its hook and called Bud at an airfield hangar. After a brisk conversation, he hung up, grinning contentedly.

At one o'clock Bud came bursting into Tom's laboratory. "Snap to, skipper!" he announced. "You have company!"

Tom looked up from his work in surprise.

"Ta-daaa!" Bud sang out, imitating a trumpet flourish.

Sandy and Phyl Newton marched in, smiling.

"Boy, this is a surprise!" Tom got up to greet them. "A mighty pleasant one. But what's the occasion?"

"The occasion is that you're coming on a mountain hike with us, out in the nice fresh air and sunshine!" Sandy informed him.

"And please don't argue," Phyl said with a giggle. "It's for your own good—not to mention ours."

"I suppose Chow Winkler put you up to this." Tom grinned.

"Never mind that," Sandy said sternly. "Just come along quietly. It's a beautiful day."

Tom glanced at his workbench cluttered with drawings and electronic gear. "Well, okay, since you're twisting my arm," he agreed. "I guess it might clear my brain at that."

"Now you're talking." Bud clapped Tom on the back and propelled him toward the two girls, who promptly seized his arms before he might change his mind.

On their way to the door, however, the telephone rang. Tom insisted upon answering it, in spite of the girls' scolding.

"Tom Swift Jr. talking."

"This is Chief Slater, Tom," said the voice at the other end of the line. "Dimitri Mirov wants to see you. I don't know what's up, but he might be ready to tell something worth while. Could you drop by?"

"Sure thing, Chief. Right away!" Tom hung up, excited by the thought that the Brungarian might be about to reveal an important secret. "Mind stopping by police headquarters first?" he asked his friends.

Minutes later, Bud's red convertible pulled up in front of the gray stone building. Tom jumped out and dashed up the granite steps.

"I've had Mirov transferred to a cell by himself," Chief Slater said as he took Tom back to see him. "Figured he might talk more freely away from his pals."

The prisoner, however, showed no eagerness to do so at Tom's arrival. He remained slouched on his bunk as the young inventor pulled a chair up to the cell bars. His only response was a slight curl of the lips.

"Have you heard about my country's new submarine?" Mirov inquired after Chief Slater left.

Tom nodded curtly.

"When are you going to build one?" Mirov prodded slyly.

"Look!" Tom snapped. "You asked to see me. Here I am. What is it you want?"

Mirov shrugged with a look of amusement. "To make a bargain with you," he replied casually. "I know the secret of that sub. Get me and my friends released and I'll give it to you."

Tom had no intention of doing so, but he parried the offer, hoping to draw Mirov out further. The prisoner, however, would say nothing more.

At last Tom gave up and rose to leave. "I'll think over your proposition," he said.

He heard Mirov chuckle as he walked away. Somewhat puzzled, Tom reported the conversation to Chief Slater and also telephoned the plant to inform Ames.

Then he hurried back to the car. Bud frowned upon hearing Tom's story.

"Do you think he's on the level?"

Tom shrugged as they headed out into the countryside. "I may be wrong, but the whole thing sounded fishy."

"Now look!" Sandy said severely. "If we're going to enjoy this hike, we're not going to talk about Brungarians or inventions or that lost missile. From now on, it will cost anyone five cents every time he breaks the rule!"

The boys chuckled and agreed. But agreeing proved easier than keeping the rule. Again and again, either Tom or Bud would inadvertently drop a remark about their submarine experiments or the search in the South Atlantic. By the time they had parked in the hills and started climbing, Sandy's and Phyl's pockets were jingling with coins.

"What are you going to do with it all?" Bud asked jokingly.

"Give it to us!" snapped a strange voice.

As the four young people turned with a start, they saw two men burst from the shrubbery just behind them.

Both were holding guns!



CHAPTER XVI

THE GUNMAN'S SURPRISE

Sandy and Phyl were terrified by the sudden appearance of the rough-looking pair with their drawn revolvers. Tom and Bud remained cool, eying the men warily.

"What's the big idea?" Tom asked.

"Shut up and hoist your mitts!" the bigger of the men snarled. As the boys obeyed, he muttered to his partner, "Keep these two punks covered, Mugs, while I take their cash!"

"Right, Packy! I'll watch 'em!"

Sandy and Phyl emptied their pockets. Then Packy took the boys' wallets and change.

"Now turn around and march!" Packy snapped.

Bud took the lead, followed by the two girls, with Tom bringing up the rear. They plodded up the brushy slope in silence for several minutes. Presently a weather-beaten cabin in a grove of trees came into view.

"You intend to hold us there?" Tom asked.

"You'll find out soon enough!" Packy answered. "We'll teach you to interfere with the Mirovs!"

The Mirovs! Like pieces of a jigsaw puzzle, the whole picture suddenly fell into place. It was clear to Tom now how the capture had been arranged.

The call to the jail from Dimitri Mirov had been a hoax. Its purpose had really been to get Tom away from Enterprises—thus giving the two thugs a starting point from which to follow him. The mountain hike, organized by Bud and the girls, had played right into their hands! As Tom sized up the situation, seeking a way out, the group reached the cabin.

"What are your terms for letting us go?" Tom asked their captors, stalling for time.

The man named Packy gave an ugly chuckle. "None yet," he said. "We may just decide to set the cabin on fire."

Sandy uttered a gasp as his words sank home. Phyl Newton had turned deathly pale. Packy now told his partner to unlock the cabin. Mugs stepped to the door.

At that moment Tom caught Bud's eye. It was now or never!

Tom whirled and smashed a stiff handblow to Packy's wrist, knocking the gun from his hand. Bud hurled himself on Mugs.

Taken off guard, the shorter thug staggered and went down under a hail of punches. Bud grabbed his wrist and twisted it mercilessly while he pinned him to the ground.

Mugs screeched with pain. "C-c-cut it out!"

"Then drop your gun!" Bud snapped.

Tom, meanwhile, had followed up his first advantage with a stunning blow to the solar plexus. Packy grunted for breath, then came back viciously with several well-aimed punches that staggered Tom.

As the young inventor stumbled backward, Packy dived for his gun. Though still groggy, Tom managed to kick the weapon out of reach. Before Packy could straighten up, Tom followed with a sweeping uppercut that caught him squarely on the chin.

Packy went down like a felled tree!

Tom picked up the gun before his groaning victim could recover. By this time, Bud had pounded his own opponent into submission. Within a few moments, both thugs were lined up against the wall of the cabin. Their wrists were tightly strapped behind them with their own belts.

"Oh ... thank goodness!" Sandy gasped.

Tom gave the girls a reassuring grin. "Are you two all right?"

"I g-guess so." Phyl gave a nervous smile.

Now that the tables were turned, it was the thugs' turn to "march." The boys herded them warily back down the hillside toward the road, where Bud had parked his red convertible. Sandy and Phyl followed close behind.



Like all cars belonging to the Swifts' key personnel, Bud's was equipped with a two-way shortwave radio. Tom switched it on and radioed Shopton Police Headquarters. Chief Slater promised to send a squad car at once.

Minutes later, they heard it approaching. Two husky police officers leaped out as the car braked to a halt, and took charge of the prisoners. Scowling and sullen, they were driven off to jail.

"Well," said Bud jokingly, "what about that relaxing hike we were starting?"

Phyl sighed. "I'm afraid you two boys just can't get away from inventions and adventures."

Sandy added, "I suggest we go home for a nice safe dinner."

Later, at the Swifts' house, Tom received a telephone call from Chief Slater. He reported that the two prisoners were known hoodlums from a nearby city.

"They claim they were hired for this job last night by a stranger who spoke with an accent," Slater went on. "According to their story, they never even got a look at his face, and they had no idea he was an enemy agent."

"Sounds reasonable," Tom agreed. "It's not likely Mirov's Brungarian henchmen would endanger their whole setup by taking any cheap gunmen into their confidence."

Chief Slater also reported that Len Unger was still at large. "But the FBI will probably pick him up soon," he added.

"I sure hope so," Tom said.

A ten-hour sleep that night proved a fine tonic. Tom awoke the next morning feeling entirely refreshed, and after a hearty breakfast, hurried off to the plant. Here he plunged into work on his quality analyzer sonar.

Much of the circuitry was assigned to the electronics department. The finished boards and sub-assemblies were fed back to Tom in his private laboratory. He himself assembled the major units.

At lunchtime, over a bowl of chili and crackers, Tom recalled another problem. "We'll need an undetectable sub to test my analyzer," he mused. "That means a repeat job of rigging all those transducers. Whew! I'd better get busy on that plastic sheathing."

As soon as he had eaten, Tom phoned Arv Hanson, who arrived at the lab in a few moments.

"You remember that idea I mentioned to Danny about molding all the transducers into a single continuous plastic sheet?" As Arv nodded, Tom went on, "Let's try it, using Tomasite as the plastic."

Tom picked up a pencil and quickly sketched out the production steps. By machine-spacing the transmitting and the receiving transducers as closely together as possible, with minimum clearance, the plastic coating could do an even better job of absorbing sonar pings than the hand-rigged model.

"And the leads from all the transducers can be combined into a single flat tape," Tom ended. "That'll make it simple to hook up with the electronic control unit inside."

"Got it, skipper," Arv said tersely. "It'll take overtime to set up the job in the plastics department. But we ought to be rolling out the sheeting Tuesday."

"That's swell, Arv! Thanks!"

By midmorning Tuesday, Tom had his quality analyzer sonar completed and was showing Bud how the units worked.

"Boy, it looks simple enough the way you explain it, prof!" Bud said admiringly. "How soon can we try it?"

"Depends on Arv," Tom replied. He picked up the phone and called the plastics department. To his delight, the sheathing was already being rolled out in quantity. Arv promised that by noon he would have enough of it available to coat a jetmarine.

"Nice going!" Tom said. "Shoot it out to the cargo-jet hangar as soon as it's ready!"

Soon after lunch, Tom, Bud, and Arv took off for Fearing Island. When they arrived at the base, the plastic coating with its myriad tiny "mikes" and "speakers" was speedily applied to a jetmarine under Arv's supervision. Tom, meanwhile, wired the control unit and also installed the analyzer sonar in the Sea Hound.

"Want to be 'It' for another underwater game of hide-and-seek?" Tom asked Bud with a grin.

"Sure, but don't tag me with a torpedo!"

Minutes later, the jetmarine slipped off into the depths with Bud and two other crewmen aboard. Tom and Arv followed in the seacopter. The quality analyzer sonar worked even better than Tom had hoped. He not only tracked the jetmarine on its outward course, but located it three different times after shutting off the analyzer long enough for Bud to seek a new location.

"How'd you like to relieve Hank in the South Atlantic?" Tom asked Bud upon their return.

Bud gave a whoop of excitement. "Roger!"

Tom slapped him on the back. "You can take off as soon as your ship's provisioned. I'll join you later—but first," Tom added mysteriously, "I have another job to attend to."



CHAPTER XVII

A MISSING AMULET

Bud's curiosity was instantly aroused. "Don't tell me you have a new trick up your nautical sleeve to fox the Brungarians?"

Tom grinned. "That's the general idea. I hope to give hydrolung divers the same protection that your jetmarine has."

"You mean make them invisible to sonar?"

"Yes," Tom replied, "and also give them personal spy gear to probe the waters around them and spot an 'undetectable' enemy."

Bud whistled. "Do that, and I'll say you're really a magician, skipper!"

Tom himself transferred the analyzer from the Sea Hound to Bud's jetmarine. On a chance that it might become necessary to operate at greater depths—either in searching for the lost missile or in shadowing the enemy—Tom also assigned Arv Hanson the job of rigging the Sea Hound and another seacopter with his new inventions.

Four crewmen volunteered for the cruise. When the jetmarine was ready, Tom and Bud exchanged tight handshakes.

"Good luck!"

"Thanks, Tom."

The young inventor waved as Bud disappeared down the hatch. As soon as the craft had submerged, Tom went back to Shopton. That evening the Swifts were enjoying a quiet dinner at home when a loud, growling buzz shattered their mealtime conversation.

"Oh!" Sandy gasped. "The burglar alarm!"

The Swifts' house and grounds were protected by a secret magnetic field. Any intruder breaking the barrier touched off the automatic alarm system. To avoid the buzzing, the family and their close friends wore wrist watches containing tiny neutralizer coils.

"I'll see who it is," Tom said, and hurried to the door, feeling a twinge of apprehension.

Was this a new attempt by Brungarian agents?

He switched on the porch light and peered out cautiously through the one-way glass pane in the door. A slim, hatless figure in a dark suit was just coming up the steps. Tom gave a smile of relief.

It was Harlan Ames!

"Hi, Harlan!" Tom opened the door before Ames had a chance to ring the doorbell. "We heard you coming!"

The security chief was startled when he realized he had activated the alarm system.

"That's strange," he said uneasily. "Tom, I wonder if—"

He broke off to dart a quick glance at his wrist. Then his face relaxed into a look of chagrin.

"Great! I forgot my wrist watch!" he murmured. "Haven't visited your house in so long I neglected to wear it."

The other Swifts smiled in amused relief, and Mrs. Swift invited him to join them for dessert. Ames, however, declined politely.

"Thank you, but I just finished dinner myself," he explained. "I dropped by to—"

Once again Ames's voice trailed off in midsentence, as he reached into the side pocket of his coat.

"My amulet!" he gasped. "It's gone!"

"Are you sure?" Tom said with quick concern.

Ames nodded as he frantically tried all his other pockets. The electronic amulet to which he referred had been issued to all Enterprises personnel and family visitors who used the private gate. The amulets were contained in slender bracelets and were designed to trap radar impulses. This prevented them from showing up as blips on the giant detector radarscope mounted on the main building. The purpose of the scope was to reveal unauthorized visitors or spies.

"My bracelet broke this afternoon," Ames said. "I slipped it into my pocket to have it repaired. But it's not there now!"

Tom grabbed a flashlight and dashed outside for a hasty check of the walk. Ames followed, to look inside his black sedan. But the amulet did not come to light.

"Did you go home after you left the plant today?" Tom asked.

Ames shook his head worriedly. "No, I stopped at a restaurant. Mind if I use your phone?"

"Go ahead."

The security chief called Enterprises and asked his assistant, Phil Radnor, who was on night duty, to make a thorough search. While awaiting the results, Ames also called the restaurant, but learned that no such item had been turned in.

Half an hour later Radnor called back to report no luck. "The amulet may show up yet, Harlan," he said. "But I'll alert the guards at the plant to be on the lookout for an unauthorized visitor."

"Thanks, Phil." Ames hung up and turned away from the telephone with an embarrassed look. "Fine example I'm setting as head of plant security," he murmured. "Let's hope the amulet wasn't stolen."

Excusing themselves from Mrs. Swift and Sandy, Tom Sr. and Jr. retired with Ames to Mr. Swift's study to discuss the news he had brought.

"I had a late call from Admiral Walter this evening," Ames explained. "The Navy's getting pretty desperate over that lost missile. They're ready to co-operate with any moves you care to make. I take it you're prepared to carry out a search on your own, Tom?"

The young inventor nodded. "Yes, as soon as I've perfected all the gear I'll need—which won't be long, I hope."

Ames added, unhappily, that certain papers and news commentators had been making snide remarks about the Swifts' failure to match the Brungarians' submarine achievement.

"I think Tom has that situation pretty well in hand," Mr. Swift remarked with a smile.

Tom gave Ames a full report on his own apparatus for rendering a submarine invisible to underwater detection. Ames grinned at the news. The grin grew even wider as he heard of the successful test of the quality analyzer sonar.

"Bud Barclay's on his way to the South Atlantic right now with a fully equipped jetmarine," Tom ended.

The next morning he eagerly tackled the job of adding sonar protection and sonar detection features to his electronic hydrolung. What an amazing fish man the wearer would be, Tom thought, if his project succeeded!

It would enable a skin diver to operate indefinitely under water at jet-propelled speed—invisible to enemy "eyes," yet be able to spy out any hostile undersea prowlers, including supposedly "undetectable" submarines!

Tom chuckled wryly as he mulled over the difficulties ahead. "Bud wasn't kidding when he said it would take a magician!"

Besides his mask, electronic breathing device, density-control unit, and ion drive, the wearer would now need at least three major additions—first, sonar-blinding equipment with electronic control; second, amplifying equipment to camouflage the wearer's noise under water; and, third, a portable quality analyzer sonar.

"Whew! The miniaturizing job alone will be a king-sized headache!" Tom said to himself. "I'd better start with a skin-diving suit made of that molded plastic Arv is turning out."

After having some of the Tomasite sheathing, with its embedding transducers, sent over from the plastics department, Tom cut out a suit from a pattern and welded the seams electronically. He had just finished wiring the control unit when Chow wheeled in a lunch cart.

"Got some deelicious steak-and-kidney pie today," the cook announced, setting it out.

"Swell," Tom said absent-mindedly.

Chow frowned but left without interrupting the young inventor. Twenty minutes later the cook poked his head into the laboratory again. Tom had not yet touched his lunch.

"Brand my vitaminnies, start eatin', boss!"

"Sure, Chow."

By this time, however, Tom had become so absorbed in the task of assembling some tiny monolithic blocks for the computer circuits of his analyzer, that the lunch remained untasted. When Chow returned a third time, Tom was startled by his bellow:

"Get your nose out o' that work, buckaroo, and eat!"

Realizing Tom's pie had cooled off, Chow had brought another serving, hot from the oven. Seeing the stern look on the Texan's face, Tom burst out laughing and obeyed meekly.

"I declare!" Chow chuckled. "One o' these days I'll have to force-feed you if you won't pay no mind to your own nourishment!"

"Sorry, old-timer." Tom smiled. "Sometimes I do get a bit wrapped up, I guess."

Hour after hour, Tom stayed glued to his workbench, sometimes busy with delicate electronic gear, sometimes lost in thought as he pondered a tricky problem in circuit design. It was long after dark when he drove home from the experimental station, yet he was back on the job in his laboratory early the next morning.

By lunchtime Tom had all the apparatus assembled. He was just trying on the plastic suit, with all its accompanying paraphernalia, when Chow made his usual appearance.

"Great sufferin' snakes!" the cook gasped. "You ain't goin' divin' in that getup, I hope! You look like a Christmas tree, boss!"

Tom nodded glumly. "Know something, Chow? That's just what I was thinking myself."

The young inventor's suit was loaded down with the various electronic units and festooned with wires. Even taking a few steps around the lab convinced Tom that the design was too unwieldy.

"I'd probably either get tangled in seaweed or sink from sheer weight," he muttered.

Changing back to his slacks and T shirt, Tom began eating abstractedly as Chow hovered around.

"If fishes could talk, I reckon you'd scare 'em half to death in that rig!" Chow said, trying to cheer Tom.

"Fish do talk," the young inventor said. "At least they make noises. Don't you remember that emergency fish-talk code we used when we were—"

Suddenly Tom paused, his mouth dropping open. "Chow! You've just solved my problem!" he exclaimed.

"I have?" Chow goggled at the young inventor.

"You sure have!" Tom bounced off his stool and began pacing about. "Now, take porpoises. They utter all sorts of sounds—grunts, squeals, jawclaps—and one particularly characteristic sound, like the grating of a rusty hinge."

Chow scratched his chin uncertainly. "Wal, what about it?"

"Suppose I used that rusty-hinge noise to mask the diver's noise." Tom turned and stabbed the air with his finger. "I could also use that same sound output as the search pulse for my quality analyzer sonar!"

In this way, Tom explained, he could eliminate part of his bulky equipment and do an even better job of making the diver "invisible."

Bubbling with enthusiasm, Tom decided to buy a live porpoise at once and make an exact recording of its sounds. As soon as he had finished lunch, he put in a number of calls to suppliers of marine specimens. But none could provide a porpoise on short notice.

"Guess I'll have to catch one myself!" Tom told Chow.

He drove out to the airfield and took off in a Whirling Duck for Fearing Island. At the base, both Mel Flagler and Zimby Cox were eager to accompany the young inventor when he told them about the trip he had in mind.

Tom chose the Sea Hound as the fastest and best suited craft for his purpose. With Mel's and Zimby's help, he quickly rigged a plastic "tank" in the stern cabin. Minutes later, the seacopter zoomed skyward, heading for the Florida Keys.

The flight was a short one at transonic speed. Tom chose a sparkling stretch of open water, a mile or so offshore from a palm-green islet. Zimby agreed to stay aboard and tend ship while Tom and Mel went over the side in hydrolungs.

The two glided about in the translucent blue depths, keeping in close range of each other. The sea was alive with shimmering fish of every hue, darting among the coral. Suddenly, as Tom veered around to rejoin Mel, his eyes widened in horror.

A vicious-looking hammerhead shark was zeroing in, directly behind his friend!

"Look out!" Tom yelled over his microphone.



CHAPTER XVIII

SMILEY THE SEA COW

Mel turned in the nick of time. The monster shark was bearing down on him like an undersea express train. Overcoming a moment of panic, Mel gunned his ion drive to dodge the attack.

As Tom watched in agonized suspense, he saw the shark's jaws open and shut in a lightning snap at Mel's outstretched arm. Its razor-sharp teeth missed their target by inches!

Mel's gasp of relief was audible over Tom's earphones. "Let's get out of here!" he cried, arrowing away from the man-killer.

Suddenly Tom realized the full extent of their peril. A long, sweeping coral reef, which extended above water, lay between them and the Sea Hound. Unless they could round the reef in time, the shark had them trapped!

"Quick! This way!" Tom exclaimed.

The shark was moving at blinding speed. As if sensing the boys' plan of escape, it launched itself in a wide curving sweep to cut them off.

"We can't make it!" Tom gasped. "We'll have to fight!"

Both swimmers were armed with skin diver's knives as a precaution. The two maneuvered to meet the killer's onslaught.

This time its broad nightmarish head was aiming straight at Tom. He jetted off to the right, but the monster veered instantly. Its lashing tail gave Mel a stunning blow.

As the shark's jaws gaped for a bite, Tom zoomed underneath the man-eater and slashed its belly with his knife.

The shark, maddened, thrashed the water in a frenzy. Tom moved like lightning to dodge a deadly blow from its bony tail. Again and again they felt the horrifying brush of the killer's fins or armor-tough hide. By this time, Mel had revived. Repeatedly the two boys dived to jab and slash at the shark's soft underbelly.

Both were nearly exhausted when the monster at last went limp and floated slowly up toward the surface. Pale with shock and fright, Tom and Mel jetted back to the Sea Hound.

Zimby Cox was startled by their faces when they clambered aboard and ripped off their masks. "What happened to you two?"

Tom told him. "Good night!" Zimby cried out.

After resting, Tom and Mel dived in again. This time luck was with them. In less than twenty minutes they sighted a small porpoise.

"Think we can lure it back toward the Sea Hound?" Mel queried.

"We'll try," Tom replied.

The creature with the bottle-shaped snout was as friendly and playful as most of its fellow dolphins. Too playful, Tom concluded, after vainly trying to tease it into chasing them. Instead of following, it would "tag" Tom or Mel quickly, then swim away, evidently expecting to be chased in turn!

"I give up!" Mel snorted in disgust.

Tom grinned and bobbed to the surface. He waved his hand several times in a prearranged signal. Zimby at last spotted him and brought the Sea Hound to the scene.

Raising his mask, Tom called, "Let's have the net!"

Zimby lowered a nylon net and some pieces of fish to the two swimmers as they came alongside. With the food as bait they tried to lure the porpoise to the seacopter. But just as they thought they had it, the monster would scoot off.

"It's just laughing at us!" Mel fumed.

At last, after winning its confidence with several bits of fish, the boys succeeded in snaring the porpoise. Tom clambered onto the Sea Hound's deck and helped Zimby haul their catch aboard. "Quacking" reproachfully, it was lowered through the hatch and placed in the tank, which was then pumped full of salt water.

As soon as the Sea Hound arrived at Fearing, Tom phoned Chow Winkler at Enterprises and asked him to fly out to the base.

"Pardner, how'd you like to ride herd on this critter and gentle it down for me?" Tom asked, when he showed Chow the porpoise.

It had been transferred to a huge, glass-paneled tank which had been set up just outside Tom's Fearing Island laboratory during his flight to the Florida Keys.

"Reckon I kin try makin' friends with it," Chow declared.

The porpoise stared morosely at Chow. The kindly old Texan's heart was touched by the odd creature. To his delight, it soon responded to his friendly overtures and quickly recovered its good nature. By the next morning the porpoise was playing catch with Chow, or else swimming over to have its back scratched. The cook named it Smiley.

"She's kind of a sea cow," he told Tom, "and you got to talk to my Smiley like any cow!" Tom grinned and refrained from explaining to Chow that a real "sea cow" was a walrus.

Meanwhile, the young inventor was busy with his own experiments. By means of a microphone placed in the tank, he made exact recordings of Smiley's "talk." Using Mel Flagler as a subject, Tom also tape-recorded the sound of a skin diver propelled through the water by ion drive.

The next step was to compare the sound pattern of the tapes. Tom filtered out the difference in the two sounds with the correlation calculator unit of one of his quality analyzer sonars.

"Uh-huh. So you got the difference betwixt Smiley's talk an' the noise Mel made," muttered Chow as he watched the jagged lines of light flashing on the pulse-check oscilloscope. "Now what're you fixin' to do with it?"

"This will be fed into the diver's sonar along with his own noise output," Tom said, "to make him sound like a porpoise."

Chow howled. "That I've got to hear!"

The young inventor worked feverishly throughout the day and into the next, perfecting his new "porpoise sonar." Using microelectronic components, he was able to reduce all the units to amazingly small size.

Next, Tom began tailoring himself a completely new skin-diving suit. Mask, ion-drive jet, and the various hydrolung units were molded into the plastic, with no loose wires or tubes showing.

Monday morning he was ready to try the outfit. The sonarscope with its tiny viewing screen was strapped to his left forearm. Another small unit was fastened to the inside of his wrist, with four plungers in finger-tip reach.

"What in tarnation's that?" Chow asked.

"Simplified controls," Tom explained. "One's for breathing adjustment, one's for the density unit, one is my ion-drive 'throttle,' and this last is for the sonar pulse—which will duplicate the porpoise sound."

The suit worked perfectly in a tank test. Chow was amazed as he listened to Tom gliding about, via an underwater microphone.

"If that don't beat all!" he declared. "Can't tell the difference 'twixt you an' Smiley!"

As Tom emerged from the tank, the portly cook rolled up his own pantlegs and waddled up the metal ladder to the tank brim. He summoned the porpoise with a whistle and straddled its back.

"What in the name of aquanautics do you think you're doing?" Tom gasped.

"I'll show you a real broncobustin' act in the water," Chow bragged.

Smiley glided off gently at first, Chow fanning the air with his hat and yipping like a rodeo star. He did, in fact, cling to his slippery perch with considerable skill.

But suddenly Smiley began bobbing and humping like an eel. Chow's face froze in alarm. A moment later the porpoise dived and the cook let out a yell of terror, "He-e-elp!"

Roaring with laughter, Tom dived in and rescued him. "Guess he ain't quite broke yet, pardner!"

"Reckon not."

Now that Tom had all his technical problems solved, he plunged eagerly into the job of fitting out his expedition to the South Atlantic to search for the lost Jupiter missile.



Besides the Sea Hound and the other diving seacopter which had already been rigged with antisonar and antidetection equipment, Tom ordered a large cargo jetmarine to be similarly equipped.



Then he drew up a list of supplies and underwater search gear needed for the missile hunt. Tom phoned orders to a dozen different departments. Food, space-plant pills, extra clothing, tools, including a midget atomic earth blaster, grappling hooks—nothing was overlooked.

"I'd better take along a Damonscope too," Tom reflected. "Judging by those Navy reports, ordinary Geiger counters haven't revealed anything."

Tom's Damonscope, one of his early inventions, was a photographic device which worked on fluorescent principles. It was amazingly sensitive to any form of radioactivity—and the missile, of course, would be "hot" from exposure to cosmic rays.

Meanwhile, Tom had ordered his new hydrolung suit, with its four-plunger control unit and porpoise sonar, to be flown back to Enterprises. Arv Hanson had promised to make up several duplicates with a team of technicians working on all-night shifts.

Late the next afternoon Tom returned to the mainland to confer with his father. Mr. Swift reviewed the expedition plans with approval.