After all the tension of preparing for it, the trip out seemed interminable.

They were all impatient to reach their destination. During blastoff and accelleration they had watched Mars dwindle to a tiny red dot; then time seemed to stop altogether, and there was nothing to do but wait.

For the first eight hours of free fall, after the engines had cut out, Tom was violently ill. He fought it desperately, gulping the pills Johnny offered and trying to keep them down. Gradually the waves of nausea subsided, but it was a full twenty-four hours before Tom felt like stirring from his cot to take up the shipboard routine.

And then there was nothing for him to do. Greg handled the navigation skilfully, while Johnny kept radio contact and busied himself in the storeroom, so Tom spent hours at the viewscreen. On the second day he spotted a tiny chunk of rock that was unquestionably an asteroid moving swiftly toward them. It passed at a tangent ten thousand miles ahead of them, and Greg started work at the computer, feeding in the data tapes that would ultimately guide the ship to its goal.

Pinpointing a given spot in the Asteroid Belt was a gargantuan task, virtually impossible without the aid of the ship's computer to compute orbits, speeds, and distances. Tom spent more and more time at the viewscreen, searching the blackness of space for more asteroid sightings. But except for an occasional tiny bit of debris hurtling by, he saw nothing but the changeless panorama of stars.

Johnny Coombs found him there on the third day, and laughed at his sour expression. "Gettin' impatient?"

"Just wondering when we'll reach the Belt, is all," Tom said.

Johnny chuckled. "Hope you're not holdin' your breath. We've already been in the Belt for the last forty-eight hours."

"Then where are all the asteroids?" Tom said.

"Oh, they're here. You just won't see many of them. People always think there ought to be dozens of them around, like sheep on a hillside, but it just doesn't work that way." Johnny peered at the screen. "Of course, to an astronomer the Belt is just loaded ... hundreds of thousands of chunks, all sizes from five hundred miles in diameter on down. But actually, those chunks are all tens of thousands of miles apart, and the Belt looks just as empty as the space between Mars and Earth."

"Well, I don't see how we're ever going to find one particular rock," Tom said, watching the screen gloomily.

"It's not too hard. Every asteroid has its own orbit around the sun, and everyone that's been registered as a claim has the orbit charted. The one we want isn't where it was when your Dad's body was found ... it's been travelling in its orbit ever since. But by figuring in the fourth dimension, we can locate it."

Tom blinked. "Fourth dimension?"

"Time," Johnny Coombs said. "If we just used the three linear dimensions ... length, width and depth ... we'd end up at the place where the asteroid was, but that wouldn't help us much because it's been moving in orbit ever since the Patrol Ship last pinpointed it. So we figure in a fourth dimension ... the time that's passed since it was last spotted ... and we can chart a collision course with it, figure out just where we'll have to be to meet it."

It was the first time that the idea of time as a "dimension" had ever made sense to Tom. They talked some more, until Johnny started bringing in fifth and sixth dimensions, and problems of irrational space and hyperspace, and got even himself confused.

"Anyway," Tom said, "I'm glad we've got a computer aboard."

"And a navigator," Johnny added. "Don't sell your brother short."

"Fat chance of that. Greg would never stand for it."

Johnny frowned. "You lads don't like each other very much, do you?" he said.

Tom was silent for a moment. Then he looked away. "We get along, I guess."

"Maybe. But sometimes just gettin' along isn't enough. Especially when there's trouble. Give it a thought, when you've got a minute or two...."

Later, the three of them went over the computer results together. Johnny and Greg fed the navigation data into the ship's drive mechanism, checking and rechecking speeds and inclination angles. Already the Dutchman's orbital speed was matching the speed of Roger Hunter's asteroid ... but the orbit had to be tracked so that they would arrive at the exact point in space to make contact. Tom was assigned to the viewscreen, and the long wait began.

He spotted their destination point an hour before the computer had predicted contact ... at first a tiny pinpoint of reflected light in the scope, gradually resolving into two pinpoints, then three in a tiny cluster. Greg cut in the rear and lateral jets momentarily, stabilizing their contact course; the dots grew larger.

Ten minutes later, Tom could see their goal clearly in the viewscreen ... the place where Roger Hunter had died.

It was neither large nor small for an asteroid, an irregular chunk of rock and metal, perhaps five miles in diameter, lighted only by the dull reddish glow from the dime-sized sun. Like many such jagged chunks of debris that sprinkled the Belt, this asteroid did not spin on any axis, but constantly presented the same face to the sun.

Just off the bright side the orbit-ship floated, stable in its orbit next to the big rock, but so small in comparison that it looked like a tiny glittering toy balloon. And clamped on its rack on the orbit-ship's side, airlock to airlock, was the Scavenger, the little scout ship that Roger Hunter had brought out from Mars on his last journey.

While Greg maneuvered the Dutchman into the empty landing rack below the Scavenger on the hull of the orbit-ship, Johnny scanned the blackness around them through the viewscope, a frown wrinkling his forehead.

"Do you see anybody?" Tom asked.

"Not a sign ... but I'm really looking for other rocks. I can see three that aren't too far away, but none of them have claim marks. This one must have been the only one Roger was working."

They stared at the ragged surface of the planetoid. Raw veins of metallic ore cut through it with streaks of color, but most of the sun-side showed only the dull gray of iron and granite. There was nothing unusual about the surface that Tom could see. "Could there be anything on the dark side?"

"Could be," Johnny said. "We'll have to go over it foot by foot ... but first, we should go through the orbit-ship and the Scavenger. If the Patrol ship missed anything, we want to know it."

The interior of the orbit-ship was dark. It spun slowly on its axis, giving them just enough weight so they would not float free whenever they moved. Their boots clanged on the metal decks as they climbed up the curving corridor toward the control cabin.

Then Johnny threw a light switch, and they stared around them in amazement.

The cabin was a shambles. Everything that was not bolted down had been ripped open and thrown aside.

Greg whistled through his teeth. "The Major said the Patrol crew had gone through the ship ... but he didn't say they'd wrecked it."

"They didn't," Johnny said grimly. "No Patrol ship would ever do this. Somebody else has been here since." He turned to the control panel, flipped switches, checked gauges. "Hydroponics are all right. Atmosphere is still good; we can take off these helmets. Fuel looks all right, storage holds ..." He shook his head. "They weren't looting, but they were looking for something, all right. Let's look around and see if they missed anything."

It took them an hour to survey the wreckage. Not a compartment had been missed. Even the mattresses on the accelleration cots had been torn open, the spring-stuffing tossed about helter-skelter. Tom went through the lock into the Scavenger; the scout ship too had been searched, rapidly but thoroughly.

But there was no sign of anything that Roger Hunter might have found.

Back in the control cabin Johnny was checking the ship's log. The old entries were on microfilm, stored on their spools near the reader. More recent entries were still recorded on tape. From the jumbled order, there was no doubt that marauders had examined them. Johnny ran through them nevertheless, but there was nothing of interest. Routine navigational data; a record of the time of contact with the asteroid; a log of preliminary observations on the rock; nothing more. The last tape recorded the call-schedule Roger Hunter had set up with the Patrol, a routine precaution used by all miners, to bring help if for some reason they should fail to check in on schedule.

There was no hint in the log of any extraordinary discovery.

"Are any tapes missing?" Greg wanted to know.

"Doesn't look like it. There's one here for each day-period."

"I wonder," Tom said. "Dad always kept a personal log. You know, a sort of a diary, on microfilm." He peered into the film storage bin, checked through the spools. Then, from down beneath the last row of spools he pulled out a slightly smaller spool. "Here's something our friends missed, I bet."

It was not really a diary, just a sequence of notes, calculations and ideas that Roger Hunter had jotted down and microfilmed from time to time. The entries on the one spool went back for several years. Tom fed the spool into the reader, and they stared eagerly at the last few entries.

A series of calculations, covering several pages, but with no notes to indicate what, exactly, Roger Hunter had been calculating. "Looks like he was plotting an orbit," Greg said. "But what orbit? And why? Nothing here to tell."

"It must have been important, though, or Dad wouldn't have filmed the pages," Tom said. "Anything else?"

Another sheet with more calculations. Then a short paragraph written in Roger Hunter's hurried scrawl. "No doubt now what it is," the words said. "Wish Johnny were here, show him a real bonanza, but he'll know soon enough if...."

They stared at the scribbled, uncompleted sentence. Then Johnny Coombs let out a whoop. "I told you he found something! And he found it here, not somewhere else."

"Hold it," Greg said, peering at the film reader. "There's something more on the last page, but I can't read it."

Tom blinked at the entry. "'Inter Jovem et Martem planetam interposui,'" he read. He scratched his head. "That's Latin, and it's famous, too. Kepler wrote it, back before the asteroids were discovered. 'Between Jupiter and Mars I will put a planet.'"

Greg and Johnny looked at each other. "I don't get it," Greg said.

"Dad told me about that once," Tom said. "Kepler couldn't understand the long jump between Mars and Jupiter, when Venus and Earth and Mars were so close together. He figured there ought to be a planet out here ... and he was right, in a way. There wasn't any one planet, unless you'd call Ceres a planet, but it wasn't just empty space between Mars and Jupiter either. The asteroids were here."

"But why would Dad be writing that down?" Greg asked. "And what has it got to do with what he found out here?" He snapped off the reader switch angrily. "I don't understand any of this, and I don't like it. If Dad found something out here, where is it? And who tore this ship apart after the Patrol ship left?"

"Probably the same ones that caused the 'accident' in the first place," Johnny said.

"But why did they come back?" Greg protested. "If they killed Dad, they must have known what he'd found before they killed him."

"You'd think so," Johnny conceded.

"Then why take the risk of coming back here again?"

"Maybe they didn't know," Tom said thoughtfully.

"What do you mean?"

"I mean maybe they killed him too soon. Maybe they thought they knew what he'd found and where it was ... and then found out that they didn't, after all. Maybe Dad hid it...."

Johnny Coombs shook his head. "No way a man can hide an ore strike."

"But suppose Dad did, somehow, and whoever killed him couldn't find it? It would be too late to make him tell them. They'd have to come back and look again, wouldn't they? And from the way they went about it, it looks as though they weren't having much luck."

"Then whatever Dad found would still be here, somewhere," Greg said.

"That's right."

"But where? There's nothing on this ship."

"Maybe not," Tom said, "but I'd like to take a look at that asteroid before we give up."

They paused in the big ore-loading lock to reclamp their pressure suit helmets, and looked down at the jagged chunk of rock a hundred yards below them. In the lock they had found scooters ... the little one-man propulsion units so commonly used for short distance work in space ... but decided not to use them. "They're clumsy," Johnny said, "and the bumper units in your suits will do just as well for this distance." He looked down at the rock. "I'll take the center section. You each take an edge and work in. Look for any signs of work on the surface ... chisel marks, Murexide charges, anything."

"What about the dark side?" Greg asked.

"If we want to see anything there, we'll either have to rig up lights or turn the rock around," Johnny said. "Let's cover this side first and see what we come up with."

He turned and leaped from the airlock, moving gracefully down toward the surface, using the bumper unit to guide himself with short bursts of compressed CO₂, from the nozzle. Greg followed, pushing off harder and passing Johnny halfway down. Tom hesitated. It looked easy enough ... but he remembered the violent nausea of his first few hours of free fall.

Finally he gritted his teeth and jumped off after Greg. Instantly he knew that he had jumped too hard. He shot away from the orbit-ship like a bullet; the jagged asteroid surface leaped up at him. Frantically he grabbed for the bumper nozzle and pulled the trigger, trying to break his fall.

He felt the nozzle jerk in his hand, and then, abruptly, he was spinning off at a wild tangent from the asteroid, head over heels. For a moment it seemed that asteroid, orbit-ship and stars were all wheeling crazily around him. Then he realized what had happened. He fired the bumper again, and went spinning twice as fast. The third time he timed the blast, aiming the nozzle carefully, and the spinning almost stopped.

He fought down nausea, trying to get his bearings. He was three hundred yards out from the asteroid, almost twice as far from the orbit-ship. He stared down at the rock as he moved slowly away from it. Before, from the orbit-ship, he had been able to see only the bright side of the huge rock; now he could see the sharp line of darkness across one side.

But there was something else....

He fired the bumper again to steady himself, peering into the blackness beyond the light-line on the rock. He snapped on his helmet lamp, aimed the spotlight beam down to the dark rock surface. Greg and Johnny were landing now on the bright side, with Greg almost out of sight over the "horizon" ... but Tom's attention was focussed on something he could see only now as he moved away from the asteroid surface.

His spotlight caught it ... something bright and metallic, completely hidden on the dark side, lying in close to the surface but not quite on the surface. Then suddenly Tom knew what it was ... the braking jets of a Class I Ranger, crouching beyond the reach of sunlight in the shadow of the asteroid....

Swiftly he fired the bumper again, turning back toward the orbit-ship. His hand went to the speaker-switch, but he caught himself in time. Any warning shouted to Greg and Johnny would certainly be picked up by the ship. But he had to give warning somehow.

He tumbled into the airlock, searching for a flare in his web belt. It was a risk ... the Ranger ship might pick up the flash ... but he had to take it. He was unscrewing the fuse cap from the flare when he saw Greg and Johnny leap up from the asteroid surface.

Then he saw what had alarmed them. Slowly, the Ranger was moving out from its hiding place behind the rock. Tom reached out to catch Greg as he came plummeting into the lock. There was a flash from the Ranger's side, and Johnny Coombs' voice boomed in his earphones: "Get inside! Get the lock closed, fast ... hurry up, can't waste a second."

Johnny caught the lip of the lock, dragged himself inside frantically. They were spinning the airlock door closed when they heard the thundering explosion, felt the ship lurch under their feet, and all three of them went crashing to the deck.