"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 a.n.a.lyzer 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 quant.i.ty. 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 a.n.a.lyzer 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 a.n.a.lyzer 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 a.n.a.lyzer 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 a.n.a.lyzer 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 a.s.signed 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 gla.s.s 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."