‘That doesn’t give you the right to know me.’ I saw a chance to get the upper hand. ‘Listen to me, L’Eesh. I think I know what’s going on here.’

Know your prey. This was my first pit, but I had prepared myself. The Ghosts seem to use only a small number of pit types - our flitter had been designed to cope with some of the common variants - and when Pohp sent us her cryptic message, I knew what she must have been talking about.

Vacuum energy: even in ‘empty’ space there has to be some energy, a ground energy level, because of quantum uncertainty. What was important for us was the effect this had - and the effect of the Ghosts’ tinkering.

‘Think of an atom,’ I said. ‘Like a little solar system with the electrons as planets, right? But what keeps a negative electron out of the positive nucleus?’

‘Vacuum energy?’

‘Right. The electron, and everything else, is surrounded by a sea of vacuum energy. And as fast as the electron loses energy and tries to spiral in, the vacuum sea supplies some more. So the electron stays in orbit.’ I peered up at the complicated sky. ‘Those weapons extracted some of the vacuum energy from the substance of our flitter. Or lowered the level of the background, so the vacuum energy drained away: something like that. All the electrons spiralled in, and molecular structures fell apart.’

L’Eesh listened, his face unreadable. Presumably he knew all this. His silence was more impressive than my babbling, even to me.

We walked on.

I felt naked without a weapon. I dug around among a thick patch of bones. I found a long, thin shaft that might have been a thigh-bone. I cracked it against a rock; it splintered, leaving a satisfactorily vicious point. As we walked I put myself through elementary drill routines.

A spear will take down a Ghost, but you have to be careful. The key resource you get from a Ghost is his hide - a perfectly reflective heat trap, with a thousand applications. Now that Ghosts are so rare, wild hides are a luxury item. People sell little squares and triangles of hide for use as charms, curios: this was, after all, a lucky species that survived the death of its sun, so the story goes.

Anyhow if you come at a Ghost with a jabbing weapon, you should try to get your spear into the carcase along the spin axis, where the hide is a little thinner, and you won’t rip it unnecessarily. Then you just follow the trail of excrement and blood and heat until he dies, which might take a day or two. Ghosts don’t leave spoor, my mother used to say. So you have to cut him an asshole.

L’Eesh was watching me analytically. ‘You’re, what, twenty, twenty-one? No children yet?’