With an effort, Tom forced all thoughts of failure out of his mind and concentrated on the job at hand. In an hour he had the computer program blocked out.  
Mr. Swift and several of the other scientists checked his work. Each nodded approval. By this time, the fused blip had long since disappeared from the radarscopes, indicating that the Jupiter probe missile—or what was left of it—had plunged to the ocean bottom.
 
"What's your next move, Tom?" Admiral Walter asked.
 
"No point in wasting time waiting for the computer results," Tom decided. "Suppose Bud and I fly back to Swift Enterprises and organize a search party."
 
"Good idea." As Admiral Walter extended a hand, his weather-beaten face softened. "And don't feel downhearted, son. You rate a Navy 'E' for the way you handled this operation. It would have succeeded if it hadn't been for that confounded enemy missile!"
 
"Thank you, sir." Tom managed a grateful grin, in spite of his discouragement.
 
Minutes later, the two boys embarked in a motor launch that took them to an aircraft carrier standing by in the vicinity. From the flattop they took off in a Navy jet for Shopton.
 
Meanwhile, Mr. Swift remained aboard the Recoverer to supervise the data processing. Tom, looking back from the soaring jet, could see one of the helicopters on its way to the missile ship to deliver the first batch of tapes.
 
It was late afternoon when the Navy jet touched down on the Enterprises airfield. The Swifts' sprawling experimental station was a walled, four-mile-square enclosure with landing strips, work-shops, and laboratories, near the town of Shopton. Here Tom Jr. and his father developed their amazing inventions.
 
Tom and Bud hopped into a jeep at the hangar and sped to the Administration Building, where Tom shared a double office with his father. Bud sank down into one of the deep-cushioned leather chairs, while Tom adjusted the Venetian blinds to let in the afternoon sunshine.
 
The spacious office was furnished with twin modern desks, conference table, and drawing boards which swung out from wall slots at the press of a button. At one end of the room were the video screen and control board of the Swifts' private TV network. Here and there stood scale models of their inventions, a huge relief globe of the earth, and a replica of the planet Mars.
 
"What are your plans for our search expedition, skipper?" Bud asked.
 
Tom ran his fingers through his crew cut. "Let's see. We'd better take the Sky Queen, I think, and also—"
 
Tom broke off as the desk intercom buzzed. Miss Trent, the Swifts' secretary, was on the wire.
 
"Your father's calling over the radio, Tom."
 
"Swell!" Tom flicked a switch to cut in the signal of his private telephone. "Hi, Dad! We just got back. Any news?"
 
"Yes, son. We have the computer results," Mr. Swift replied. "Got a pencil handy?"
 
Tom copied down the latitude and longitude figures as his father dictated.
 
"According to the latest hydrographic maps, based on IGY findings," Mr. Swift went on, "this area is a high plateau of the Atlantic Ridge—it's near the St. Paul Rocks."
 
"What about the depth?"
 
"It averages between a hundred and three hundred feet," said the elder scientist.
 
Tom gave a whistle. "Lucky break, eh?"
 
"Maybe and maybe not," Mr. Swift said cautiously. "The bottom there is heavily silted."
 
"Oh—oh." Tom made a wry face. "In that case, we may have some digging to do."
 
"I'm afraid so. However, no use borrowing trouble." After a short discussion, the elder scientist added, "I'll probably fly home tomorrow, son. Give my love to Mother and Sandy."
 
"Right, Dad. So long!" Tom hung up and reported the news to Bud.
 
"What kind of underwater gear will we use?" Bud inquired.
 
"I'm not sure myself," Tom admitted. "Guess we'll have to take along a variety of equipment and play it by ear."
 
Before proceeding with his search plans, Tom phoned home to inform his mother of his arrival. Mrs. Swift was sympathetic when she heard of the failure to recover the probe missile.
 
"I'm sure you'll locate it," she said encouragingly.
 
"Some of your cooking will sure help brighten the picture," Tom replied with a grin. As he put down the receiver a moment later, he told Bud, "You're having dinner with us tonight, pal. Fried chicken and biscuits."
 
Bud licked his lips. "Lead me to it!"
 
Chuckling, Tom began drawing up a list of supplies for the expedition. Bud helped with the details, after which Tom phoned the underground hangar and the Swifts' rocket base at Fearing Island to give the orders for the next day. Crewmen were also detailed for the trip.
 
It was six o'clock when the two boys finally piled into Tom's low-slung sports car and drove to the Swifts' big, pleasant house on the outskirts of Shopton. Sandra, Tom's blond, vivacious sister, greeted them at the door.
 
"About time!" she teased. "We were beginning to think you two had taken off somewhere."
 
"Think I'd leave town while you and that fried chicken are in Shopton?" Bud grinned.
 
"What a line!" Sandy's blue eyes twinkled. "I know it's the fried chicken you're really interested in."
 
"Where's the rest of that 'we' you were referring to?" Tom inquired.
 
"I'm sorry, Tom," Sandy said in a mournful voice. "Phyl couldn't make it."
 
As Tom's face fell, she burst out giggling and a second later Phyllis Newton emerged from the kitchen. Brown-eyed, with long dark hair, Phyl was the daughter of Tom Sr.'s old comrade-in-arms and lifelong chum "Uncle Ned" Newton. Like Sandy, she was seventeen.
 
"You didn't think I'd miss this rare evening, did you, Tom?" she said, laughing. "After all, it isn't often we see you two."
 
Sandy and Phyl liked to needle the boys about their infrequent dates, due to Tom's and Bud's busy schedules.
 
Mrs. Swift, slender and sweet-faced, gave Tom a hug and greeted Bud warmly. Over the delicious dinner, the conversation turned to the mysterious thief missile.
 
"Who on earth could have fired it?" Sandy asked.
 
Tom shrugged. "No telling—yet. There's more than one unfriendly country which would give a lot for the data picked up on our Jupiter shot."
 
"You aren't expecting more trouble, are you?" Phyl put in uneasily.
 
Tom passed the question off lightly in order not to alarm his mother and the two girls. But inwardly he was none too sure of what his survey expedition might encounter in trying to locate the lost probe missile.
 
Ever since his first adventure in his Flying Lab, the youthful inventor had been involved in many daring exploits and thrilling situations. Time and again, Tom had had to combat enemy spies and vicious plotters bent on stealing the Swifts' scientific secrets.
 
His research projects had taken him far into outer space and into the depths of the ocean. With his atomic earth blaster, Tom had probed under the earth's crust at the South Pole, and in other adventures he had faced danger in the jungles of Africa, New Guinea, and Yucatan. His latest achievement, receiving the visitor from Planet X, had been to construct a robot body for this mysterious brain energy from another world. Now, Tom realized, he was on the brink of another adventure which might hold unexpected dangers.
 
Early the next morning the majestic Sky Queen was hoisted from its underground hangar berth and hauled by tractor to its special runway. This mammoth, atomic-powered airplane had been Tom's first major invention. A three-deck craft, it was equipped with complete laboratory facilities for research in any corner of the globe. Jet lifters in the belly of the fuselage enabled the craft to take off vertically and also to hover.
 
As Tom supervised the loading of the equipment, a foghorn voice boomed, "'Mornin', buckaroos!"
 
The chunky figure of Chow Winkler came into view. Formerly a chuck-wagon cook in Texas, Chow was now head chef on Tom's expeditions. As usual, a ten-gallon hat was perched on his balding head and he was stomping along in high-heeled boots.
 
"Wow! A shirt to end all shirts!" Tom chuckled.
 
"Real high style, eh?" Chow twirled about to display his latest Western creation. The shirt seemed to be made of silvery fishlike scales, which glistened like a rainbow.
 
"I figured as how this was just the thing fer an ocean jaunt," Chow added with a grin. "How soon do we take off, boss?"
 
"As soon as we get the rest of this gear stowed," Tom replied.
 
Twenty minutes later the Sky Queen soared toward the ocean. Soon they came in sight of Fearing Island rocket base, a few miles off the coast. Once a barren stretch of sand dunes and scrub-grass, the island was now the Swifts' top-secret rocket laboratory, guarded by drone planes and radar. It served as the supply base for Tom's space station and as the launching area for all space flights. Seacopters and jetmarines were also berthed here.
 
A radio call from Tom brought a sleek, strange-looking craft zooming up to join them.
 
It was the Sea Hound, latest and largest model of Tom's amazing diving seacopter. It had an enclosed central rotor, powered by atomic turbines, with reversible-pitch blades for air lift or undersea diving. Superheated steam jets provided forward propulsion in either element.
 
As the Sea Hound streaked alongside the Flying Lab, two figures in the seacopter's flight compartment waved to Tom and Bud. One was Hank Sterling, the blond, square-jawed chief pattern-making engineer of Enterprises. The other was husky Arv Hanson, a talented craftsman who transformed the blueprints of Tom's inventions into working models.
 
"All set," Hank radioed. "Lead the way."
 
"Roger!" Tom replied.
 
Flying at supersonic speed, they reached the area of the lost missile in the South Atlantic soon after lunch. Already on hand were ships of the Navy task force assigned by Admiral Walter to participate in the missile search. The Sea Hound settled down on the surface of the water, while the Sky Queen hovered at low altitude nearby.
 
Tom contacted the government craft and learned that as yet no sign of the lost Jupiter prober had been detected. Then he made ready to begin his own search.
 
"Let's try the Fat Man suits first," Tom told Bud. Turning to Slim Davis, a Swift test pilot who was in the crew, the young inventor added, "Take over, will you, Slim?"
 
"Righto." Slim eased into the pilot's seat.
 
"Got a job for me, skipper?" asked Doc Simpson, Swift Enterprises' young medic.
 
"Yes. Help the boys, if you like, rig the undersea elevator, and then assemble a tractorized air dome," Tom suggested.
 
"Will do," Doc promised.
 
A ladder was dropped. Tom and Bud excitedly descended to the Sea Hound. The search for the lost missile was about to begin!
 
Once the boys were aboard, the seacopter submerged and dived quickly to the ocean floor. Tom and Bud each climbed into a Fat Man suit and went out through the air lock. The suits, shaped like huge steel eggs with a quartz-glass view plate for the operator seated within, had mechanical arms and legs.
 
The boys waddled about, the built-in searchlights of their suits piercing the murky gloom. They saw nothing but the deep accumulation of silt on the ocean bottom, which made the going difficult.
 
"This is too slow," Tom called over his sonarphone. "Let's try the air dome."
 
The dome was a huge underwater bubble of air, created by a repelatron device which actually pushed the ocean water away. The air supply inside was kept pure by one of Tom's osmotic air conditioners which made use of the oxygen dissolved in the water.
 
The air bubble, however, even with its jet-propelled platform, also proved inadequate for the research job. Its caterpillar treads repeatedly bogged down in the silt.
 
"Maybe the seacopter itself is our best bet," Bud suggested.
 
"Worth a try," Tom urged.
 
But the Sea Hound, too, had a serious drawback. Even with its powerful search beam sweeping the ocean floor as it prowled along, the explorers found their vision too limited.
 
Finally Tom said, "Bud, we could skin-dive at this depth."
 
"Let's give it a whirl," Bud urged.
 
The seacopter surfaced again, while the boys donned flippers, masks, and air lungs. Then they dropped over the side and made their way slowly downward into the gray-green depths, accustoming themselves gradually to the increased pressure.
 
"A lot more freedom of action," Tom thought. "If only we didn't have to communicate by signals!"
 
There was a sudden swoosh somewhere on his right. A projectile, Tom realized! Turning, his eyes widened in horror as he saw an uprush of bubbles.
 
Bud's air tank had been hit!