Tense, excited men gazed spaceward from the ships and planes of the South Atlantic task force. Other watchers waited breathlessly in the control room of the ship Recoverer. Among these was Tom Swift Jr.  
"How close to earth is our Jupiter probe missile?" Bud Barclay asked Tom excitedly.
 
The lanky blond youth beside him, in T shirt and slacks, shot a glance at the dials of the tracking equipment. "Eight thousand miles from this spot, Bud. It should land here in fifteen minutes!"
 
Tom Jr., his father, Bud, and a host of scientists, Navy officers, and newsmen were crowded aboard a U.S. Navy missile launching ship.
 
"Just think!" Bud exulted. "You'll have data from the planet Jupiter that no one on earth has yet been able to get!"
 
"If we recover the missile safely," Mr. Swift spoke up hopefully. The elder scientist's voice was quiet but taut with the strain of waiting. The two Swifts resembled each other closely—each had deep-set blue eyes and clean-cut features—although Tom was somewhat taller and rangier.
 
"You're right, Dad," Tom agreed. "If we don't snare the missile, our whole project will be a total loss to America's space program!"
 
At Tom's words, the watchers and crewmen who were crowded into the Recoverer's control room stirred restlessly. Its bulkheads were banked with radar and telemetering devices. Tension had been mounting throughout the morning aboard the ships and observation planes of the task force as everyone awaited the return of the planet-circling missile—scientists' deepest penetration into space so far.
 
"What do you mean, a total loss?" Bud argued. "Even if the recovery operation's a flop, the shot will still pay off in valuable information, won't it?"
 
Tom shook his head grimly. "The purpose of this unmanned, exploratory flight around Jupiter was to take and record all kinds of data. But none of the info is being radioed back to us."
 
"How come?"
 
"If we had put in radio gear strong enough to relay signals back, it would have cut down the amount of information-gathering equipment aboard," Tom explained. "We had to make every ounce count."
 
Outwardly calm, Tom was seething with inner excitement. Although only eighteen—the same age as his husky, dark-haired pal and copilot, Bud Barclay—Tom had been given the job of directing the recovery phase of the United States government's Project Jupiter survey. The Swifts and their rocket research staff had built the missile and engineered the space probe for the government.
 
"Whew!" Bud gave a nervous whistle. "I see what you mean, pal. With all our eggs in one basket, we sure can't afford to get butter-fingered with the Jupiter prober."
 
Admiral Walter, a tall, distinguished man, graying at the temples, smiled. "It's what we call in warfare a calculated risk, Bud," he said. "But with Tom in charge, I believe we have nothing to worry about."
 
Mr. Swift's eyes shone with fatherly pride at the admiral's remark. Tom Jr.'s pioneering rocket flights and inventions had won the youth a top rank in American space research.
 
"Guess you're right, sir," Bud agreed. "I'll back genius boy here any day!"
 
Tom winced as Bud whacked him heartily on the shoulder. "Better save your orchids and keep your fingers crossed, fly boy," the young inventor advised. "That rocket's not home yet."
 
Radio telescopes, both on land and aboard the ships of the task force, were following the missile's progress as it drew closer to earth. All were feeding a steady stream of information to the ships' computers.
 
"How soon will you fire the retro-rockets, Tom?" Admiral Walter inquired presently.
 
"In about ten seconds, sir," Tom replied, eying the sweep second hand of the clock.
 
Moments later, a red light flashed on the master control panel. Tom's finger stabbed a button. Far out in space, the retarding rockets in the missile's nose were triggered for a brief burst, slowing its high speed. Without this, the missile would hurtle to flaming destruction in the atmosphere.
 
"We've picked it up!" shouted a radarman.
 
Bud gave a whoop of excitement and everyone crowded around the radarscope. Tom's steel-blue eyes checked the blip. Then he threw a switch which started an automatic plotting machine that had been prepared with the landing plan, and noted that the missile was slightly off the correct path. A new flow of information now began pulsing in as other ships' tracking radars recorded its course. The data was being fed automatically to the "capture" computer. This would analyze the correct flight path for the recovery missile, which would magnetically seize the returning traveler from Jupiter and bring it safely home.
 
Tom quickly read off the results from the computer's dials, then busied himself again with the retarding-rocket controls.
 
"Everything going okay, skipper?" Bud asked.
 
Tom nodded. "I've readjusted the retarding rockets. They'll fire at the proper intervals to slow down the missile still further and bring it back on beam."
 
The excited buzz of voices in the compartment gradually quieted as the clock ticked steadily toward the next step in the recovery operation.
 
"Stand by for missile firing!" Tom snapped.
 
A seaman relayed the order over the ship's intercom. Tense silence fell as Tom's eyes followed the sweep of the second hand.
 
"All clear for blast-off!" came the talker's report.
 
Tom pressed the firing button. A split second later the listeners' eardrums throbbed to a muffled roar from topside as the slender recovery missile shot skyward. The ship rocked convulsively from the shock of blast-off. Then it steadied again as the gyros damped out the vibrations.
 
"Wow!" Bud heaved a sigh of relieved tension. Then he dashed from the compartment and up the nearest ladder for a quick look at the rocket as it disappeared into the blue.
 
Tom watched the recovery missile intently on the radarscope.
 
"Nice going, son," said Mr. Swift quietly.
 
In response to his father's reassuring grip on his arm, Tom flashed him a hasty smile. For the first time, the young inventor realized he was beaded with perspiration and that his pulse was hammering.
 
"It's a case of wait and hope," Tom murmured.
 
On every ship and plane in the task force, eyes were glued to the radar screens. Two small blips were visible—one the Jupiter probe missile, the other the recovery missile—moving on courses that would soon intersect.
 
Just as Bud returned to the compartment, several of the watchers gave startled gasps.
 
"Another blip—coming in from nine o'clock!" Admiral Walter exclaimed. "What's that?"
 
Tom stared at the new blip. It was moving steadily toward the meeting point of the first two missiles!
 
"It's a thief missile!" Tom cried out. "Some enemy's trying to steal our probe data!"
 
"Good night!" Bud gulped. "Who'd dare try that?"
 
"I don't know," Tom muttered tensely. "But if those three missiles meet, our whole project will be wrecked!"
 
"Better tape all readings!" Mr. Swift advised.
 
"Right, Dad!"
 
Admiral Walter had paled slightly under his deep tan. In stunned silence, the Navy officers and scientists watched as Tom's lean hands manipulated two controls.
 
"What are those for?" Bud asked.
 
"One's to speed up our recovery missile," Tom explained. "Looks like a slim hope, though, from the way that third blip is homing on target. This other control has just caused every instrument on this ship, and all the others in the task force, to make permanent records on magnetic tape of all their readings.
 
"If a collision occurs and the probe missile falls into the sea," Tom went on, "there's only one hope of recovery—to plot the exact geographical position and then get to the spot before the enemy does!"
 
"Roger!" Bud agreed.
 
It was obvious that Tom's fears about the missiles colliding were well founded. The mystery blip had veered as the recovery missile speeded up. Within seconds, the three blips met on the screen and fused into a single spot of light.
 
"The probe missile's no longer responding to control!" one of the telemetering scientists called out.
 
Admiral Walter, grim-faced, flashed a questioning look at Tom. "Then recovery has failed?"
 
"I'm afraid so, sir."
 
The fused blip was still visible on screen as the radar dishes tracked it, moving in a way that indicated a steep downward plunge.
 
For a moment Tom felt numb with despair. But he set his jaw firmly and turned to the admiral.
 
"Sir, I'd like helicopters readied for take-off immediately," Tom said. "As soon as the tracking instruments lose contact, have the recording tapes picked up from every ship in the task force and brought here to the Recoverer."
 
Admiral Walter nodded tersely. "Very well. Then what?"
 
"I'll get to work right now," Tom replied, "and lay out a computer program to process the readings."
 
The data—consisting of millions of information "bits" from the shipboard instrument tapes—would be fed to an electronic brain. The brain would then calculate the probable location in latitude and longitude of the sunken missile.
 
As the admiral snapped out orders, Tom exchanged a brief worried glance with his father. Each was pondering the same thought.
 
Could Tom find the lost Jupiter probe missile? Or would their enemy locate it first?