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.