The ColU swivelled its camera eyes to study Yuri. ‘You have noticed that too. About the builders. That they display curiosity.’

Yuri shrugged.

‘None of the others have noticed this, or if they have it has not been remarked to me.’

‘So what?’

‘Similarly, Yuri Eden, you try to puzzle out the transits of the inner worlds, while the others barely look up at the sky . . . You ask why I was made curious. Why are you curious, Yuri Eden?’

‘Why shouldn’t I be?’

‘The others aren’t. Not even Lieutenant Mardina Jones. You have all suffered huge trauma. You, in fact, have suffered more, having been sent away from your own time even before your exile here. And yet here you are, thinking, observing, watching the planets, the life of Per Ardua. You can speak to me openly, Yuri Eden.’

Curious about builders or not, Yuri didn’t like to look too deeply inside himself. He said uncomfortably, ‘I don’t think of it like that. It just feels like I keep getting pushed through these doors. From past to future, Earth to Mars, Mars to the Ad Astra, the Ad Astra to here. Or when things change. When people die, when Onizuka and Harry went crazy. That’s like we passed through another kind of door.’

‘And?’

He shrugged. ‘And I can’t go back. I know that. I can’t bring Lemmy back to life. I can’t go back to the past. Every door I pass through is one way. So I may as well look around, and see what there is beyond the next door, and the next.’

‘Hm. If you can’t go back, why won’t you reveal your true name to your fellow colonists?’

‘Why should I?’

‘That itself is a reaction to your past.’

He had no answer to that. They moved on for a while, walking, rolling, in companionable silence.

They came to one of the ColU’s experimental sites. This was an outcropping of rock, a black basalt, volcanic rock that had erupted in sheets from the sandy ground after some ancient magmatic event. They called this extrusion feature the Lip. Here the ColU had fenced off an expanse of bare rock, perhaps a quarter of an acre, and domed it over with a fine transparent mesh to keep out the native life. Lichen were growing busily on the naked rock, powdery white spots.

The ColU inspected this lichen garden, with sensors mounted on a manipulator arm.

‘It’s doing well,’ Yuri said.

‘I think you’re right. I’ve used a variety of lichen here, some gen-enged, some a hybrid with cousins from Mars. But some of this is transplanted straight from Earth, from Antarctica, from the high deserts, from post-volcanic landscapes where lichen such as this would be the first colonists. What remarkable organisms – and themselves complex, a symbiosis between fungi and photosynthesising bacteria. They dissolve the rock for access to nutrients like phosphorus; they grow filaments to break up the rock, and later the mosses come and grow in the dust, and then plants . . . I did not manufacture these patches of nascent soil. The lichen are doing it for themselves. How remarkable, Yuri Eden – if you’re curious about anything, be curious about this! These are the true invaders of Per Ardua, the true colonists—’

A light, in the corner of Yuri’s eye. He spun around. A spark, sulphurous orange, climbed into the sky, from above the colony. ‘That’s a flare gun.’

The ColU immediately backed off, turned, and rolled away, cutting across the bare landscape. ‘We must return. Emergency, Yuri Eden! Emergency!’ And it accelerated, soon outpacing Yuri, the pale light of Proxima gleaming from its upper dome.

CHAPTER 21

When they got back to the settlement they found Mardina and John Synge standing in the open air, facing each other, loaded crossbows raised. Mardina had a fat flare gun tucked into her waistband. They were both weeping, Yuri saw, and Mardina Jones weeping was an unusual sight.

There was no sign of Abbey Brandenstein or Matt Speith.

Not again, Yuri thought with a sinking feeling. We aren’t doing this to ourselves again.

The ColU screeched to a halt alongside him, throwing up dust. ‘Get behind me, Yuri Eden.’

‘Why?’

‘Because I think John Synge intends to kill you.’

Mardina kept her eyes on John, eyes bright with tears in the Prox light. ‘Yuri? That you?’

‘I’m here, Mardina. What’s going on? Where are Abbey and Matt?’

‘Where do you think they are? Dead. Dead in their beds. This bastard got them while they slept. He was supposed to be sentry. He was supposed to keep us safe!’

‘We must try to be calm,’ the ColU said, sounding sanctimonious.

Yuri could take in none of this. In the months since the deaths of the others, Abbey and Matt had become huge figures in his world, two of just four human beings he shared his life with. Abbey, the flawed ex-cop. Matt, bemused, ever baffled, but making his art again. Two damaged people, thrown together in a hostile world, doing their best. What else was there to life, in the end? And yet now they were gone, complications, flaws and all, gone into the dark for ever. Dispatched on an impulse by this lunatic, John Synge.

‘I don’t want to kill you, Mardina,’ John said now. ‘Can’t you see that? That’s what this is all about. You.’

‘I’ll take you down if you come a step closer.’

‘It was for you, Mardina. I wanted you!’

‘You were with Martha.’

‘But now she’s dead. And seeing you every day, so close – look, I’m not a lustful man. I never was. But you, you—’

‘My fault, was it?’ There was a hysterical edge to Mardina’s voice now. ‘If you wanted to be with me, why did they have to die?’

‘Because they were in the way. Abbey would have stopped me, and Matt would have protected Abbey, if I’d given him a chance—’

‘But you didn’t give either of them a chance, did you? And what about Yuri?’

‘I’d have picked him off on his way back to the camp, with luck. I had a plan – if you hadn’t found me – it was a chance, you see, the others asleep, Yuri out of the camp. It would have been just us, Mardina. I could make you happy.’ He took a step forward, crossbow still raised.

Mardina’s bow was wobbling. ‘No closer.’

‘But if I—’

The ColU suddenly raised a kind of pistol, and fired a single shot. It hit John in the left temple; the other side of his skull seemed to explode outward in a shower of blood and pale matter. He stood for a second, still holding the bow, shuddering. Then he crumpled, falling straight down on himself, like a collapsing tower.

The ColU said, ‘ “But if I can’t have you, then nobody will have you.” That was how that sentence was going to end, I fear. Look.’ It gripped its weapon in a claw-like projection, crushed it, held up the ruin. ‘Major Lex McGregor left this with me, against my protests, in case of contingencies like this. Now it is destroyed. See? No more guns on Per Ardua. Though it is evident,’ it said, ‘that you do not need guns to kill each other.’

Yuri walked around the ColU, and stared at the fallen body of John Synge, the splash of blood.

Mardina, trembling so violently she shook, lowered the crossbow. ‘Just the two of us, kid.’

Suddenly Yuri couldn’t deal with this. Any of it. Not even the presence of Lieutenant Mardina Jones, ISF. ‘I’m not a kid.’

‘Yuri—’

‘My name’s not Yuri.’

He turned on his heel and walked off, south, away from the camp, just walked and walked, slamming one foot into the dirt after the other, like the first time they had let him out of the shuttle and he had run away, his wrists still in plastic cuffs. Maybe he should have just kept running that day and not come back, and taken his chances alone.

He looked back once. He saw Mardina and the ColU moving slowly around the camp. Clearing up the bodies. He turned away, and walked, and walked.