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............