“No, Jeanie. Hold by, and don’t move.”

They were closing on us. Parmikan was two or three meters in the lead. Lyle still held the gun, but he had learned his lesson. He would not fire again until he was at point-blank range, too close to be thrown off in his aim by the effects of free-fall rotation.

“Mac!” We couldn’t stand still and be slaughtered like sheep. I swung to argue with him, and saw the expression on his face. He was agonized and biting his lower lip. “Mac, come on. We can’t just give in.”

But he was shaking his head at me. “I’m sorry, Jeanie,” he said. “This isn’t me. I can’t go through with it. No matter what happens next, I have to give them a chance.” And he lifted his arm towards Lyle and Parmikan. “Don’t come any closer. Stay right there. You are in terrible danger.”

That stopped them — for a second or two. They stared all around, and saw nothing. Lyle snorted through his broken nose, while Parmikan laughed aloud for the first time since I had met him.

“Don’t try that on us, McAndrew,” he said. “We weren’t born yesterday. If you stand still, I promise you’ll get yours clean and quick.”

He was moving forward again. My suit’s vision enhancement showed the grin on his shapeless mouth. He looked as happy as I had ever seen him. And then the clean white of his suit was broken by a thin black line that ran across Stefan Parmikan from hip to hip, about two inches below his navel.

He stared down at himself as the line widened. He started to scream, and tried to back up.

It was too late. His motion carried him forward. As it did so he shrank, shortening and squeezing in towards his hips. The thin black line became a rolling tunnel of red and purple across his whole body. Twisted internal organs were moving into it from above and below. Then Parmikan had passed all the way through.

The scream ended. A pair of legs, still held together at the top, came floating on towards us. Separate from it moved a torso, cleanly severed. Blood gouted out and froze as a fine icy spray.

Lyle, a few meters behind, had enough time to stop. He paused, still holding the gun.

“Hand that over.” I summoned what little energy I had and spoke over the suit radio before McAndrew had time to react. And then, when Lyle hesitated, I said, “Hand it over right now. Or get just the same as he did.”

He hardly seemed to be listening. His eyes were following the horror of Parmikan’s severed body. But he nodded and released the gun, which floated gently away from him.

It’s a measure of how far gone I was that I actually started out towards it, until McAndrew grabbed me.

“You stay where you are, too,” he said. “And Lyle, don’t move a millimeter until we come around and get you. There’s other gravitational line singularities through this whole volume.”

We began to move again, McAndrew hauling me along like ballast in a strange helical path that wound its way towards Van Lyle. Finally McAndrew was able to reach out and snag the gun.

“All right.” He waved it at Lyle, then towards the Hoatzin. “We’ve got a clear run from here to the ship. You start that way. And remember that I understand freefall ballistics a lot better than you do. I won’t miss.”

The three of us drifted slowly back to the lock, but McAndrew would not let Van Lyle enter. He handed me the gun. “You first, Jeanie. Can you fix the lock so it works?”

“I think so.” I moved inside. “I just have to reset the safety interlocks.”

I made it sound trivial, and it should have been. But I kept half blacking-out before I was done and able at last to refill the interior of the Hoatzin with air.

It seemed forever before the lock cycled again. I wondered and stayed tense. I had the gun. Suppose Lyle had taken advantage of that and overpowered McAndrew?

I dropped those worries when Lyle emerged from the inner lock. His manner and bearing were of a crushed man with no fight left in him. I made him take his suit off, but I kept my own on until McAndrew finally came through the lock.

He didn’t give Lyle a look. He came straight across to me and examined my injured leg.

“I’m sorry, Jeanie,” he said, as he helped me ease out of my suit. “I know I put us in danger, warning them the way I did. If Parmikan had stopped in time we might have been killed. But I couldn’t let them go on moving into that line singularity, without giving them at least a chance to stop. I just couldn’t do that. You’d have done the same thing, wouldn’t you?”

“Of course I would.”

Like hell. If it had been up to me, Lyle would be floating around in two halves, the same as Stefan Parmikan. But then, compared with McAndrew I’m a barbaric, vengeful throwback. “Don’t worry about it, Mac. What you did was the right thing.”

I winced, as the suit came free from my calf and caught on crusted blood. “So whose idea was it, Van Lyle?” I said. “Who decided that on this expedition, McAndrew and I wouldn’t be going back?”

He had been sitting slumped over, staring at the floor. He looked up, opened his mouth to speak, then changed his mind. He shook his head.

I didn’t blame him. When we arrived home he would be charged and surely convicted; but nothing the system authorities could do to him was half as bad as Anna Lisa Griss’s vengeance if he betrayed her.

McAndrew had gone across to the capsule’s medical center and was returning with two spray syringes. “I’m going to put you under, Jeanie, while I dress your leg,” he said. “You’ll have to wait until we’re home for a full repair. But first, to be safe…”

He went to Van Lyle and pressed the loaded syringe against the back of the stooped man’s neck. Lyle tried to stand up, with a startled expression on his face. It was already too late.

“Better if we keep him under all the way back,” Mac said, as after a few struggling seconds Lyle slid forward and fell face-down on the floor. “That way we don’t have to worry.”

I wasn’t worrying. I was going to be next, and physically I was ready for it. My calf was beginning to throb mercilessly. Still I held up my hand in protest. “Mac, wait a minute. We shouldn’t head back until you’ve finished your experiments. And you’ve hardly started.”

He moved behind me. “Don’t be daft, Jeanie. I can come here anytime. And I surely will. There’s big questions to be answered. I need to map the structure of those shadow matter objects in more detail. And now we’ve got another candidate for the hidden matter. How much is cold dark matter, how much hot dark matter, how much shadow matter?”

The cool nozzle of the syringe touched the back of my neck, and the spray diffused through my skin. I felt the effect at once as a pleasant, relaxing warmth that spread through my whole body.

“Mac,” I said, as the capsule of the Hoatzin began to blur around me. “You saved us, but I don’t know how you did it. How did you know where to go, to put that gravity singularity right between us and those two?”

“Easy enough,” he said. “I had the measurements from the mass detectors. That made it a standard problem of inverse potential theory: Given the field, where are the masses needed to generate it? I already felt sure that there were line singularities of shadow matter, ones that would work — gravitationally — on anything in our universe that encountered them. But just where were they? I worked that out while you were inside the lock, playing your fun and games with Lyle and Parmikan. Of course, I had to make simplifying assumptions and hope they wouldn’t affect the answer. And it would have been really nice to have a computer. But there was no time for that. I did what I could.”

I did what I could. What he had done, in the few minutes before I was blown out of the lock in a gust of freezing air, was to solve, mentally, a problem that would have taken me half a day to set up, and a computer to solve. And he had done it while knowing that the next half hour might end his own life.