A look of plastic relief rippled over Cassandra's face. I nodded. “Good man,” I said. I'd killed before, but I never enjoyed it.

“But, still,” said Pickover, “I would like some revenge.”

Cassandra's upper arms were still pinned by Pickover, but her lower arms were free. To my astonishment, they both moved. The movement startled me, and I looked down, just in time to see them jerking toward her groin, almost as if to protect…

I found myself staggering backward; it took a second for me to regain my balance. “Oh, my God…”

Cassandra had quickly moved her arms back to a neutral, hanging-down position — but it was too late.

The damage had been done.

“You…” I said. I normally was never at a loss for words, but I was just then. “You're…”

Pickover had seen it, too; his torso had been twisted just enough to allow him to do so.

“No woman…” he began slowly.

Cassandra hadn't wanted to touch Pickover's groin — even though it was artificial — with her bare hands.

And when Pickover had suggested exacting revenge for what had been done to him, Cassandra's hands had moved instinctively to protect—

Jesus, why hadn't I see it before? The way she plunked herself down in a chair, the fact that she couldn't bring herself to wear makeup or jewelry in her new body; her discomfort at intimately touching or being intimately touched by men: it was obvious in retrospect.

Cassandra's hands had moved instinctively to protect her own testicles.

“You're not Cassandra Wilkins,” I said.

“Of course I am,” said the female voice.

“Not on the inside, you're not,” I said. “You're a man. Whatever mind has been transferred into that body is male.”

Cassandra twisted violently. God-damned Pickover, perhaps stunned by the revelation, had obviously loosened his grip, because she got free. I fired my gun again and the bullet went straight into her chest; a streamer of machine oil, like from a punctured can, shot out, but there was no sign that the bullet had slowed her down.

“Don't let her get away!” shouted Pickover, in his rough mechanical voice. I swung my gun on him, and for a second I could see terror in his eyes, as if he thought I meant to off him for letting her twist away.

But I aimed at the nylon strap restraining his legs and fired. This time, the bullet only partially severed the strap. I reach down and yanked at the remaining filaments, and so did Pickover. They finally broke and this strap, like the first, snapped free. Pickover swung his legs off the table, and immediately stood up. An artificial body had many advantages, among them not being woozy or dizzy after lying down for God-only-knew how many days.

In the handful of seconds it had taken to free Pickover, Cassandra had made it out the door that I'd pried partway open, and was now running down the corridor in the darkness. I could hear splashing sounds, meaning she'd veered far enough off the corridor's centerline to end up in the water pooling along the starboard side, and I heard her actually bump into the wall at one point, although she immediately continued on. She didn't have her flashlight, and the only illumination in the corridor would have been what was spilling out of the room I was now in — a fading glow to her rear as she ran along, whatever shadow she herself was casting adding to the difficulty of seeing ahead.

I squeezed out into the corridor. I still had my flashlight in my pocket; I fished it out and aimed it just in front of me; Cassandra wouldn't benefit much from the light it was giving off. Pickover, who, I noted, had now done his pants back up, had made his way through the half-open door and was now standing beside me. I started running, and he fell in next to me.

Our footfalls now drowned out the sound of Cassandra's; I guessed she must be some thirty or forty meters ahead. Although it was almost pitch black, she presumably had the advantage of having come down this corridor several times before; neither Pickover nor I had ever gone in this direction.

A rat scampered out of our way, squealing as it did so. My breathing was already ragged, but I managed to say, “How well can you guys see in the dark?”

Pickover's voice, of course, showed no signs of exertion. “Only slightly better than biologicals can.”

I nodded, although he'd have to have had better vision than he'd just laid claim to in order to see it. My legs were a lot longer than Cassandra's, but I suspected she could pump them more rapidly. I swung the flashlight beam up, letting it lance out ahead of us for a moment. There she was, off in the distance. I dropped the beam back to the floor in front of me.

More splashing from up ahead; she'd veered off once more. I thought about firing a shot — more for the drama of it, than any serious hope of bringing her down — when I suddenly became aware that Pickover was passing me. His robotic legs were as long as my natural ones, and he could piston them up and down at least as quickly as Cassandra could.

I tried to match his speed, but wasn't able to. Even in Martian gravity, running fast is hard work. I swung my flashlight up again, but Pickover's body, now in front of me, was obscuring everything further down the corridor; I had no idea how far ahead Cassandra was now — and the intervening form of Pickover prevented me from acting out my idle fantasy of squeezing off a shot.

Pickover continued to pull ahead. I was passing open door after open door, black mouths gaping at me in the darkness. I heard more rats, and Pickover's footfalls, and—

Suddenly, something jumped on my back from behind me. A hard arm was around my neck, pressing sharply down on my Adam's apple. I tried to call out to Pickover, but couldn't get enough breath out… or in. I craned my neck as much as I could, and shone the flashlight beam up on the ceiling, so that some light reflected down onto my back from above.

It was Cassandra! She'd ducked into one of the other rooms, and lain in wait for me. Pickover was no detective; he had completely missed the signs of his quarry no longer being in front of him — and I'd had Pickover's body blocking my vision, plus the echoing bangs of his footfalls to obscure my hearing. I could see my own chilled breath, but, of course, not hers.

I tried again to call out to Pickover, but all I managed was a hoarse croak, doubtless lost on him amongst the noise of his own running. I was already oxygen-deprived from exertion, and the constricting of my throat was making things worse; despite the darkness I was now seeing white flashes in front of my eyes, a sure sign of asphyxiation. I only had a few seconds to act—

And act I did. I crouched down as low as I could, Cassandra still on my back, her head sticking up above mine, and I leapt with all the strength I could muster. Even weakened, I managed a powerful kick, and in this low Martian gravity, I shot up like a bullet. Cassandra's metal skull smashed into the roof of the corridor. There happened to be a lighting fixture directly above me, and I heard the sounds of shattering glass and plastic.

I was descending now in maddeningly slow motion, but as soon as I was down, Cassandra still clinging hard to me, I surged forward a couple of paces then leapt up again. This time, there was nothing but unrelenting bulkhead overhead, and Cassandra's metal skull slammed hard into it.

Again the slow-motion fall. I felt something thick and wet oozing through my shirt. For a second, I'd thought Cassandra had stabbed me — but no, it was probably the machine oil leaking from the bullet hole I'd put in her earlier. By the time we had touched down again, Cassandra had loosened her grip on my neck as she tried to scramble off me. I spun around and fell forward, pushing her backward onto the corridor floor, me tumbling on top of her. Despite my best efforts, the flashlight was knocked from my grip by the impact, and it spun around, doing a few complete circles before it ended up with its beam facing away from us.