“We’ll stay behind Hilda for a day or so,” Davydov said. “Then back to work.” He heaved out a breath, grinned at us. “Time to get out of here.”

When the relieved celebration was over, and I had calmed down, I went into my room and fell into a deep sleep. Just before I woke up, I had a vivid dream:

I was a child, on Mars, and we were playing hide-and-seek, as we often did. We were at the station on Syrtis Major, on one of those broad desert plains that are strewn with boulders — boulders from the size of basketballs up to the size of a small room, all scattered across the plain in a regular pattern that used to baffle our elders. “There’s no way such even distribution could be natural,” my father would say, sitting on one of the rocks and staring out at the nearby horizon. “It looks like a stage set.”

But to us children it was perfectly natural. And in the late afternoons, after dinner, we would play hide-and-seek. In my dream it was near sunset, one of the dust sunsets, when you could look straight at the little red sun, and the sky was ribbed with pink bands of dust, and the rust-colored plain was marked by long black shadows, one for each rock. I was hiding behind a spherical boulder about waist-high, crouched down, watching the other kids make their dashes for home base. Home base was a long way away. I could see the wind, picking up swirls of sand, but in my suit I couldn’t feel it. There were giggles and quick breathing on the radio band, which was turned down so that the sounds were all very quiet. My mike was turned off. The person who was it gave up; there were too many boulders, too many shadows. “Olly olly oxen, free free free,” she called, singing the phrase in a quavering voice. “Olly olly oxen, free free free.”

But I couldn’t come in. There was another it, something I didn’t recognize, a tall dark thing like one of the long black shadows come alive. It was nearly sunset, the ruby sun was touching the old crater wall to the west. I was hiding in earnest. I could just dare to put one eye over the rock, to see the dark shape move around, looking behind one rock after the other. Where was home base? The radio transmitter hissed. No one called. The dark thing that was it was moving toward my hiding place, checking boulder after boulder. The shadow of the crater wall was stretching across the plain, blacking out everywhere…

I shifted against the bed, half woke for a moment. Then my father had me by the hand. We were free of suits, under the dome. I was younger, about seven. We were walking across the baseball diamond. Dad had our gloves and the ball, one of the kids’ softballs that wouldn’t go very far when you hit it. “When I was your age and played baseball,” Dad told me, “the field was about the same size as this one.”

“This one’s little.”

“On Mars it is. But on Earth even the grown-up balls wouldn’t go very far when you hit them.”

“Because of gravity.” Whatever that meant.

“Right. The Earth pulls harder.” He gave me my glove and I stood behind home plate. He stood on the pitcher’s mound and we threw the ball back and forth. “That pitcher really got you yesterday.”

“Yeah. Right on my kneecap.”

Dad grinned. “I saw how you hung in there the next time you got up. I like that.” He caught and threw. “But why did you try to steal third when you had just been hit on the knee?”

“I don’t know.”

“You were out by a mile.” He fielded a low one. “And Sandy had just bunted and got out to get you to second. And once you’re on second you’re in scoring position.”

“I know,” I said. “I just took off when I got a good lead.”

“You sure did.” Dad was grinning, he threw a hard one at me. “That’s my Emma. You’re awful fast. You could probably steal third, if you worked hard enough. Sure. We work hard at it, you could be a real speedster…”

And then I was running, across the open desert, the hard-baked oxidized sand of south Syrtis. In my dream the broad plain was like the Lazuli Canyon, filled with breathable air. I ran barefoot, in my gym shorts and shirt. In Mars’s gentle grasp I bounded forward, arms making a sort of swimming motion, as my father had taught me. No one had really worked on running in Martian gravity; I was working it out for myself, with Dad’s help. I was in some sort of race, far ahead of the others, pushing off the warm gritty sand with great shoves of my thighs, feeling the thin chill air rush by. I could hear my father’s voice: “Run, Emma, run!” And I ran across that red plain, free and powerful, faster and faster, feeling like I could run over the horizon before me and on forever, all the way around the planet.

Nadezhda and Marie-Anne woke me coming through the door, talking of excess biomass. My heart was thumping, my skin was damp. In my mind I still heard my father’s voice. “Run!”

They began working incessantly to complete the starship. Nadezhda and Marie-Anne stayed up to all hours in our room, poring over programs and program results. It was laughable, really, for having missed them the Committee police weren’t likely to pass that way again. Nevertheless they hurried, and my roommates grew more and more serious as days passed.

“…Degree of closure of any substance is established by its rate of consumption in the system, E, and the rate of flow in incomplete closure, e,” Nadezhda would mutter, as if praying, glancing balefully at me as I refused to work with them for more than several hours a day. The lights focused on the little desk, Marie-Anne hunched over the computer screen, copying down figures… “The substance’s closure coefficient K is determined by K equals I minus e over E…”

And closure for the whole system was a complex compilation of the degrees of closure for all the substances being recycled. But they could not get that master coefficient high enough, do what they might. I tried hard to figure out something myself. But perfect closure is not natural, it does not exist anywhere, except perhaps in the universe as a whole. Even there, no doubt each big bang is a little bit smaller… In the starship, the leaks would be in waste recycling. They couldn’t deal with the accumulation of chlorides, or the accumulation of humic matter in the algal reactors. And they wouldn’t be able to completely recycle corpses, neither animal nor human. Certain minerals… if only they could be re-introduced into the system, made useful to something which would transform them into something back in the mainstream of the cycle… So we worked, for hours and hours, mutating and testing bacteria, juggling the physiochemical processes, trying to make a tail-in-mouth snake that would roll across the galaxy.

One night when they were gone I typed out the full program and filled in estimated figures of my own, to find the point where the accumulations would imbalance the system enough to break it down. I got about seventy years.

It was an impressive achievement, given what they were given, but the universe is a big place, and they needed to do better.

One day while thinking about this problem of closure, a week or more after the fly-by, Andrew Duggins, Al Nordhoff, and Valenski stopped me in the hall. Duggins looked fat and unhealthy, as if the situation were taking its toll on him.

“We hear that you helped the mutineers evade a Committee police fleet that came near here,” he accused.

“Who told you that?” I said.

“It’s the talk of the ship,” he said angrily.

“Among whom?” I asked.

“That doesn’t matter,” Valenski said in his clipped, accented English. “The question is, did Committee police pass us by while we three were incarcerated last Friday?”

“Yes, they did.”

“And you were instrumental in making the plans to hide from them?”

I considered it. Well, I had done it. And I wanted to be known for what I was. I stared Valenski in the eye. “You could say that, yes.” A strange feeling, to be in the open-