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."
