The alert signal in the laboratory buzzed. Tom snapped on the radio to the Swifts' space station. The caller sounded urgent. "Message for the Swifts! Message for Tom Senior or Tom Junior!"
       "Tom Junior here. What's up?"
       "Emergency! Ghosts on one of Saturn's moons and heading this way! Come at once!"
       "Ghosts! What sort of ghosts?" Tom demanded.
       The radio voice replied, "Our observatory has spotted some strange objects on Mimas. They're too indistinct to identify. You'd better get up here fast!"
       "Will do!"
       As Tom turned off the radio, his father walked in. The eighteen-year-old inventor bore a strong resemblance to his famous parent. Tom Junior was a bit taller, but both had the same athletic build, deep-set blue eyes, and blond hair.
       After Mr. Swift had been briefed on the radio conversation, he said, "We'd better go to the space station at once and try to figure out these ghostly figures. Let's see if they're really a menace before notifying Washington."
       "I'm ready," said Tom. "I'll call Bud."
       Bud Barclay, the same age as Tom, was a flier who went on all Swift expeditions. He was muscular, black-haired, and full of humor. Within minutes he arrived at the lab and was told about the trip.
       "Ghosts!" he exclaimed. "Sounds like a space nightmare. When do we leave?"
       "Pronto," Tom replied.
       It was dusk when the three drove through the Swift Enterprises complex to the airfield and took off for Fearing Island, a thumb-shaped stretch of sand dunes and scrubgrass off the Atlantic Coast. Here the Swifts had established a launching area for rockets.
       Tight security governed the island. When the alarm siren sounded, radar tracked unfamiliar objects. At night giant searchlights crisscrossed the sky with stabbing beams, and robot drone planes circled constantly to intercept spying intruders. An electrified guard net screened the beaches at all times.
       A rocket ship, ready of lift-off, stood on a launch pad. Mr. Swift and the boys climbed into space suits and Tom took the controls. There was a deafening roar and the ground vibrated as the myriad of repelatrons lifted and the mammoth craft from its pad. One of Tom's most important inventions, these selective matter repellers sent a powerful downward thrust of repulsion beams. The great ship arced into the sky for a rendezvous with the space station, which was in a orbit 22,000 miles above Loonaui Island south of Hawaii.
       Bud settled back in his seat for the trip. "I suppose you'll use your megascope space prober to get a good look-see at those ghosts."
       He was speaking of Tom's invention, an electronic telescope of potentially infinite range. By adjusting two waves to cancel each other at a given point, one could get a clear picture at any distance.
       "We'd better be prepared to do something about the ghosts," Mr. Swift warned. "It's possible they're dangerous!"
       Some time later the Swift space station hove in sight. Magnetized to it was the Atomic Spider-Crab. This radio-controlled device could be sent out to catch objects in space by means of large claws at the ends of its two arms. Along its belly were spinnerets through which Tomasite thread could be ejected and quickly spun around the person or rocket to be retrieved.
       "Any stranded astronaut would be thankful to have that mechanical crustacean rescue him," Bud observed.
       Tom agreed. "Even our automatic Comet Catcher might assist if the helpless man, or a stray space object, came near enough."
       The Comet Catcher was a gigantic Tomasite net that moved around the hull of the space station. It was powered by repelatrons––instruments that repelled atomic radiation while generating counterradiation.
       "Tom," said Bud, looking at the station's two telescopes, "I see your astronomers are still keeping an eye on the Blue Planet."
       "Mother Earth? Why not, Bud? She's the most beautiful planet in the solar system."
       Tom eased his rocket ship into the space station hangar, and the three passengers emerged into a hum of activity. A service crew was preparing a rocket for blastoff. Engineers, wearing magnetized boots, walked across the hull testing engines for metal fatigue.
       "I'd like to get my fingers into some of that oily debris," Tom muttered. He always wanted to join in when a motor was being checked out.
       "No time," Bud reminded him. "The ghosts are waiting for us."
       The boys and Mr. Swift took an elevator to the observatory, where Tom's megascope space prober was located.
       John Peterson, chief astronomer, came forward. "Boy, am I glad to see you!" he exclaimed. "Here! Take a look at this planetary dance!"
       Tom sat down at the controls of the megascope space prober, snapped on the electronic circuitry, twisted the dials, and zoomed in on Mimas.
       Steamy, dancing masses appeared, forming a circle of bright spots with darker areas between them. They began to pulsate rhythmically, fading into dimness, and then growing brighter until they were vivid once more.
       "Wow!" Tom exclaimed. "I've never seen anything like this, including the iridescent gas we found on our own moon. How about you, Dad?"
       "No, son, I haven't. And I'm sure John will bear me out that this phenomenon is unknown to all the sciences!"
       The chief astronomer nodded vigorously to show he was as baffled as the others. "For a while they were coming closer, but they've gone back toward Mimas again," he said.
       "What kind of substance do you figure those things are made of?" Bud asked.
       Tom shook his head. "That's the mystery, Bud. It's impossible to tell their composition." He paused, then added slowly, "Photo-Essence might be the best description until we find out more."
       "How will we do that?" Bud queried. "Take a whirl through space in the Cosmotron?"
       The Cosmotron Express, designed by Tom Junior, had made several voyages into the solar system and was on round-the-clock alert for future trips.
       "Let's try our space friends," Tom answered. "They may have some info on the ghosts."
       The Swifts' space friends had introduced themselves by means of an interplanetary projectile that had crash-landed at Enterprises. The young inventor had decoded geometric markings on the missile, indicating a message. Using the same system he had sent back messages by high-power transmission. Two-way communication had resulted.
       Gradually, by adding symbol to symbol and word to word, Mr. Swift had compiled a large space dictionary. He and his son could now carry on extended communication with their planetary friends.
       As Tom started to compose a message, Bud, who was looking through a porthole, gave a hoarse shout. "A meteor!" he yelled. "A giant meteor! It's headed straight for us!"
       "The Comet Catcher must be out of commission!" Tom gasped. "Hit the deck!"


       A terrific crash rocked the space station as the meteor struck it a glancing blow before deflecting into space. Tom rose and watched the others get to their feet.
       "We're lucky no one got hurt," he said. "Let's find out what happened to the Comet Catcher."
       He and Bud rounded up workmen to make a check inside the station, and found a malfunction in the repelatron system.
       "The meteor must have hit this brace," Bud stated.
       Tom surveyed the twisted metal. "You're right, Bud. It's been jammed against this other one, neutralizing the power. No wonder the net wouldn't open. We can fix it easily. Hand me that electronic crowbar."
       Tom forced the bar under the damaged brace and injected a burst of electricity. The pressure drove the strut back to normal position.
       Tom turned off the juice. "Now the net will operate," he told the work crew, "but we'll have to replace that repelatron." He pointed. "Just prop it up until we can finish the job."
       Bud asked, "What about the station's hull, Tom? I know it's made of Tomasite, but it took a tremendous wallop from that meteor. Think the hull might have cracked under the impact?"
       "We can't take any chances, even with Tomasite," Tom replied. "I'll go out and look."
       He donned a space suit made of wire fiber and coated with a layer of synthetic rubber. A zippered hood and goggles protected his face. With a good flow of oxygen, the suit guaranteed survival in space for several hours. Communication was maintained by means of a transiphone in the helmet.
       Tom shuffled along a dimly lighted gangway and edged through a porthole on the "rim" of the space station "wheel." He began to clamber over the hull, using a long pole with a hook on the end to probe for breaks in the superplastic.
       "Terrific!" he told himself after a thorough inspection. "That meteorite left us with a paint job to do, but thank goodness there are no cracks. Dad's Tomasite is really something!"
       Before going inside, Tom paused for a look around. Out of the starry background a silvery shape emerged––a rocket ship whizzing toward the space station. It was on a collision course!
       Quickly Tom radioed a warning, "Veer off!"
       Back came the chilling reply, "Out of control!"
       Frantically Tom contacted Bud and told him to trigger the Comet Catcher into action. As the ship was about to plunge head-on into the station, the net swept upward and caught the rocket.
       At the same instant the net brushed Tom from the hull. He began to float off helplessly into space!