“Give me a second.” Wenig’s fingers flew over the console again. If he ever decided that he didn’t want to work at the Penrose Institute, he’d make the best space-racer in the System.

He looked at the output for a second, frowned, and said, “I think I must have made an error.”

“Why?”

“I’m coming up with a distance from the surface of about nine thousand kilometers. That means the Merganser would be feeling a pull of fifty gee — their drive would be full on, as high as it’s designed to go. It wouldn’t make sense for them to hang there like that, on full drive. Want to go on down to them?”

“No. Hold it where we are.” I leaned back and closed my eyes. “There has to be a pattern to what Mac’s been doing. He went right through the System back there with the drive full on, now he’s hanging close in to a high-density object with the drive still full on. What the hell’s he up to?”

“You won’t find out unless we can get in touch with him.” Wenig was sounding impatient again. “I say we should go on down there. Now we know where he is it’s easiest to just go and ask him.”

It was hard to argue with him, but I couldn’t get an uneasy feeling out of the back of my head. Mac was holding a constant position, fifty gees of thrust balancing the fifty gee pull of HC-183. We couldn’t get alongside him unless we were willing to increase Dotterel’s drive to a matching fifty gee.

“Give me five more minutes. Remember why I’m here. It’s to keep you from doing anything too brave. Look, if we were to hang on our drive with a twenty gee thrust, how close could we get to the Dotterel?”

“We’d have to make sure we didn’t fry them with our drive,” said Wenig. He was busy for a couple of minutes at the computer, while I tried again to make sense of the pieces.

“We can get so we’re about sixty thousand kilometers from them,” said Wenig at last. “If we want to talk to them through the microwave radar link, the best geometry would be one where we’re seeing them side-on. We’d have decent clearance from both drives there. Ready to do it?”

“One minute more.” I was getting a feeling, a sense that everything that McAndrew had done had been guided by a single logic. “Look, I asked you what would happen if the drive failed when the life-capsule was up close to the mass disk, and you said the system would move the capsule back out again. But look at it the other way round now. Suppose the drive works fine — and suppose it was the system that’s supposed to move the life-capsule up and down the column that wouldn’t work? What would that do?”

Wenig stroked at his luxuriant mustache. “I don’t think it could happen, the design looked good. If it did, everything would depend where the capsule stuck.”

“Suppose it stuck up near the disk, when the ship was on a high-thrust drive.”

“Well, that would mean there was a big gravitational acceleration. You’d have to cancel it out with the drive, or the passengers would be flattened.” He paused. “It would be a bugger. You wouldn’t dare to turn the drive off — you’d need it on all the time, so that your acceleration compensated for the gravity of the disk.”

“Damn right. If you couldn’t get yourself farther from the disk, you’d be forced to keep on accelerating. That’s what happened to the Merganser, I’ll bet my pension on it. Get the designs of the capsule movement-train up on the screen, and let’s see if we can spot anything wrong with it.”

“You’re an optimist, Captain Roker.” He shrugged. “We can do it, but those designs have been looked at twenty times. Look, I see what you’re saying, but I find it hard to swallow. What was McAndrew doing when he came back through the system and then out again?”

“The only thing he could do. He couldn’t switch the drive off, even though he could turn the ship around. He could fly off to God knows where in a straight line — that way we’d never have found him. Or he could fly in bloody great circles, and we’d have been able to see him but never get near to him for more than a couple of minutes at a time — there’s no other manned ship that could match that fifty gee thrust. Or he could do what he did do. He flew back through the System to tell us the direction he was heading, out to HC-183. And he balanced here on his drive tail, and sat and waited for us to get smart enough to figure out what he was doing.”

I paused for breath, highly pleased with myself. Out of a sphere of trillions of cubic miles, we had tracked the Merganser to its destination. Wenig was shaking his head and looking very unhappy.

“What’s wrong,” I said cockily. “Find the logic hard to follow?”

“Not at all. A rather trivial exercise.” He looked down his nose at me. “But you don’t seem able to follow your own ideas to a conclusion. McAndrew knows all about this ship. He knows it can accelerate at the same rate as Merganser. So your idea that he couldn’t fly around in big circles and wait for us to match his position can’t be right — the Dotterel could do that.”

He was right.

“So why didn’t Mac do that? Why did he come out all this way?”

“I can only think of one answer. He’s had the chance to look at the reason the life capsule can’t be moved back along the axis, so the drive mustn’t be switched off. And he thinks that this ship has the same problem.”

I nodded. “See now why I wouldn’t let you take the Dotterel all the way up to fifty gee?”

“I do. You were right, and I would have taken us into trouble if you hadn’t been along. Now then” — Wenig looked gloomier than ever at some new thought — “let’s take the logic a step farther. McAndrew is hanging down there near HC-183 in a fifty gee gravity field. We can’t get there to help him unless we do the same, and we’re agreed that we dare not do that, or we’ll end up with the same difficulty that he has, and we won’t be able to turn off the drive.”

I looked out of the port, toward the dark bulk of HC-183 and the Merganser, hovering on its plume of high-temperature plasma. Wenig was right. We daren’t go down there.

“So how are we going to get them out?”

Wenig shrugged, “I wish I could tell you. Maybe McAndrew has an answer. If not, they’re as inaccessible as if they were halfway to Alpha Centauri and still accelerating. We’ve got to get into communication with them.”

When I was about eleven years old, just before puberty, I had a disturbing series of dreams. Night after night, for maybe three months, I seemed to wake on the steep face of a cliff. It was dark, and I could barely see handholds and toeholds in the rock.

I had to get to the top — something was hidden below, invisible behind the curve of the black cliff face. I didn’t know what it was, but it was awful.

Every night I would climb, as carefully as I could; and every night there would come a time when I missed a handhold, and began to slide downwards, down into the pit and the waiting monster.

I woke just as I reached the bottom, just as I was waiting for the first sight of my pit beast.

I never saw it. Puberty arrived, sex dreams replaced my fantasy. I forgot all about the cliff face, the terror, the feeling of force that could not be resisted. Forgot it totally — except that dream memories never disappear completely, they lie at some deep submerged level of the mind, until something pulls them out again.

And here I was again, back on the same cliff face, sliding steadily to my fate, powerless to prevent it. I woke up with my heart rate higher by thirty beats a minute, with cold perspiration on my forehead and neck. It took me a long time to return to the present, to banish the bygone fall into the pit.

I finally forced myself up to full consciousness and looked at the screen above me. The purple blaze of a plasma drive danced against the black backdrop of HC-183 and its surrounding star field. It hung there, falling forever but suspended on the feathery stalk of the drive exhaust. I lay there for about ten minutes, just watching, then looked across at Wenig. He was staring at me, his eyes unblinking.