As the Sea Hound returned to Fearing Island from its search for Bud's jetmarine, Tom was beside himself with worry. Had his experiment cost the lives of his best friend and the other crewmen aboard?  
"I'll never forgive myself if anything's happened to them!" Tom muttered bleakly.
 
Hank Sterling squeezed the young inventor's arm. "You know Bud's high spirits, skipper," he said. "He may have taken off on some crazy lark."
 
"Sure! A whale hunt, maybe!" Arv Hanson wisecracked, trying to lighten the gloom.
 
Tom forced a grin, but he remained heavy-hearted as they neared the base. His only hope now was that a radio message from the jetmarine might have been picked up while they were gone.
 
As soon as the seacopter was moored, Tom leaped ashore. The crewmen on the docks had no news to report, so Tom piled into a jeep with Arv and sped off to the Fearing communications center. Hank remained aboard the Sea Hound to secure all gear.
 
Churning along the graveled road, Tom and Arv passed the launching area. Huge, needle-nosed cargo rockets and the mighty spaceship Titan loomed against the sky. Tom's moon-voyaging Challenger and his more recent space craft the Cosmic Sailer were also based there.
 
"Going to alert the Navy for a search?" Arv inquired as they reached the communications building.
 
Tom nodded and braked the jeep to a screeching halt. "Coast Guard too. They can pass the word to commercial shipping to be on the lookout."
 
A telephone rang as he hurried into the office.
 
"For you," the clerk said, looking up at Tom. "Nice timing!"
 
Tom grabbed the phone. His face widened into a grin. "Bud! You seagoing jet stream! What happened?"
 
Arv grinned, too, in relief.
 
"Your antidetection gear worked so well we vanished right out of the ocean!" Bud replied with a chuckle. Turning serious, he reported how his jetmarine had trailed the mysterious intruder and how he and Mel had captured the two Brungarian frogmen and their shore contact.
 
"Nice going, pal!" Tom exclaimed.
 
"But here's the catch," Bud went on. "When we took off again in our hydrolungs to go back aboard ship, the jetmarine was gone!"
 
"Maybe she's trailing the enemy sub," Tom conjectured.
 
"That's what I'm hoping," Bud said uneasily. "Trouble is, our subs aren't armed, and who knows about that Brungarian job? The way they sling missiles around, anything could happen if she spots the jetmarine."
 
Tom frowned. "I'll organize a search right away. Where are you calling from?"
 
"Police headquarters at Sandbank."
 
"Okay. Take it easy, and I'll send a whirlybird to pick you up," Tom promised.
 
"And don't forget some clothes," Bud added with a chuckle. "Mel and I are getting chilly."
 
"Right!" Tom hung up and gave Arv Hanson a quick briefing.
 
Then he phoned the base airfield to dispatch a helicopter. He also contacted the nearest Coast Guard station and put through a long-distance call to Navy Headquarters in Washington to request help in searching for the jetmarine. Finally he and Arv headed back to the submarine docks in the jeep.
 
A flurry of activity followed as Tom detailed ships for the search and rounded up crews. He was interrupted by a phone call in the loading shed. It was the control-tower operator.
 
"One of our drone planes has spotted a sub approaching, skipper," the operator reported.
 
"What bearing?" Tom demanded excitedly.
 
"One-seven-six." Tom was about to hang up and grab a pair of binoculars when the operator added hastily, "Wait! It's responding to our radio challenge!... That's ours, all right!"
 
Tom dashed out of the shed and scanned the sea to the southward. Sure enough, a jetmarine had surfaced and was speeding toward the sub docks. Minutes later, Tom was shaking hands warmly with Zimby Cox and Mack Avery.
 
"Is Bud okay?" was Zimby's first question.
 
"Right! I just heard from him," Tom replied. "He and Mel captured those enemy frogmen and a copter's on the way to pick them up. What happened to you fellows?"
 
Zimby confirmed Bud's guess that they had taken off in pursuit of the enemy craft.
 
"We figured Bud and Mel could make out on their own," Zimby explained. "And we thought the sub's course or actions might tip us off to its nationality. Also, if it tried any sabotage or mine-planting, we could radio the Navy."
 
Instead, Cox went on, the mysterious craft had proceeded to a point about ten miles offshore where it rendezvoused with another submarine.
 
"And get this, skipper!" Mack Avery put in. "The other sub was undetectable! We were close enough to get a peek at it, but we couldn't ping it on the sonarscope."
 
"That figures," Tom said grimly. "Those frogmen were apparently Brungarians."
 
Zimby Cox related that a man had transferred from the undetectable submarine to the one they had been following. The first sub had then headed out to sea, as if to cross the ocean back to its home base. The other had departed on a course toward the South Atlantic.
 
"Probably back to the lost missile area. At least that's the way we figured it," Zimby added.
 
"And neither sub spotted you?" Tom questioned.
 
Zimby grinned wryly. "We might not be here if they had detected us. But I'm pretty sure they didn't. Anyhow, they gave no sign."
 
Tom was doubly elated at the news. His antidetection gear had evidently worked perfectly in a showdown test with the enemy, even at close range. Moreover, if the second sub was returning to the South Atlantic, it seemed likely that the enemy, too, had not yet located the precious missile with its data from Jupiter.
 
"You guys rate Navy medals," Tom told Zimby and Mack jubilantly. "Come on back to Shopton with me and I'll buy you the juiciest steaks in town!"
 
Before leaving the base, Tom called the Coast Guard and the Navy to cancel h............