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 p.r.o.nounced 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, ap.r.o.ned figure of Chow Winkler entering.

"Hi, boss! Can I borrow a radio?" Chow asked. "Kinda like a lil music while I wra.s.sle 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 k.n.o.b and the tw.a.n.gy 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 pa.s.sed 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!"