We rode for another hour or so, until the tunnels opened up into a wider cavern, and the gurzas slowed to a stop. This must be a rest spot of some sort—I could see the blackened remnants of a fire on the cave’s floor, beneath one of the round holes opening up to the surface.

This time, Nadin was too tired to argue with me. She didn’t resist as I helped her off Thork’s back. I braced her weight against my shoulder until she could sit on a large, flat-topped boulder. She drank some water, and when I handed her a blanket from her pack, she bundled herself in it and drifted quickly off to sleep.

The sky through the ceiling holes was turning a deep magenta. It was hard to tell with Iamos’ weird, thin atmosphere, but I guessed it had to be close to sunset. I moved through the large cavern, looking up at intervals to see what I could of the sky above. If I stood at the right angle, I could just make out the edge of that yellow moon I’d seen my first night here.

Nadin had said it was Venus. But that was impossible. Venus orbited between Mercury and Earth, more than a hundred million kilometers away. On Mars in my time, you could only see Venus at certain times of the year, and it was never closer or brighter than a big star. Jupiter was a lot bigger—sometimes you could even make out the stripes of its atmosphere—but nowhere near the size of this. This was bigger than Phobos and Deimos combined.

I’d thought about it last night, lying awake in the hospital after that riot in the citidome. I vaguely remembered my eighth-grade science teacher saying something about Venus’ poles being upside down, about it rotating backward. Nobody knew why or how, but there was speculation that something had happened to Venus—like a super-huge asteroid collision that had knocked it out of its orbit. What if its orbit in my time wasn’t its original orbit? What if… something had happened to it?

I hadn’t thought anything about it at the time, other than a bland, Huh, that’s interesting. But now it seemed like the worst disaster imaginable. I didn’t know when that impact was slated to happen—but I did know that it would punch a big hole in the geroi’s “evacuate to Hamos” plan. And if the whole population of Iamos had already evacuated to Venus when the impact hit…

I couldn’t tell Nadin. Not after the way she flipped out when she found out I wasn’t actually some far-distant descendant of the Iamoi. And maybe I was wrong. Maybe I’d misunderstood something.

But still. Ceilos’ parents were up there, and who knew how many other people. Yeah, the geroi were creepy, but I didn’t want anyone to die.