They reached the gate to the Dutchman's launching slot and entered.

Inside the ship Tom and Johnny strapped down while Greg made his final check-down on the engines, gyros and wiring. The cabin was a tiny vault, with none of the s.p.a.cious "living room" of the orbit-ships. Tom leaned back in the accelleration cot, and listened to the count-down signals that came at one minute intervals now. In the earphones he could hear the sporadic chatter between Greg and the control tower. No hint that this was anything but a routine blastoff....

But there was trouble ahead, Tom was certain of that. Everybody on Mars was aware that Roger Hunter's sons were heading out to the Belt to pick up where he had left off. Greg had secured a leave of absence from Project Star-Jump ... unhappily granted, even though his part in their program had already been disrupted. Even they had heard the rumors that were adrift....

And if there was trouble now, they were on their own. The Asteroid Belt was a wilderness, untracked and unexplored, and except for an almost insignificant fraction, completely unknown. If there was trouble out there, there would be no one to help.

Somewhere below the engines roared, and Tom felt the weight on his chest, sudden and breath-taking.

They were on their way.

4. "Between Mars and Jupiter...."

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 pa.s.sed 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 s.p.a.ce 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 s.p.a.ce 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...o...b..t 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 pa.s.sed 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 s.p.a.ce and hypers.p.a.ce, 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...o...b..tal 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 s.p.a.ce to make contact. Tom was a.s.signed 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 cl.u.s.ter. 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...o...b..t 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.