Mardina nodded. ‘I see – I think. Which happened to be a history in which Rome survived, as it did not in your history.’

‘That’s it,’ Earthshine said. ‘So the destiny of the human race is altered fundamentally. Billions who might have lived were never born at all. Billions more rise up to take their place. And those billions strive to extend the Hatch network, long before it would have happened in the earlier reality – for that, you see, was the point.’

Titus frowned. ‘But if this is true, what of the other histories, other realities? Are they simply discarded, like – like early drafts of a note of command?’

‘Not discarded,’ said Earthshine. ‘They all continue to exist, out there, somewhere in the multiverse. And all, incidentally, will be terminated at the End Time; they are too closely related to be spared. But there is only ever one universe that is primal. As if it is more real than the rest. And before the Dreamers’ meddling, the primal universe would have been the most logical, the most neat, the most self-consistent in terms of causality. Self-consistent as the others were not.

‘Magnificent it may be, but this project of the Dreamers is – untidy. Only the original primal universe was clean in a causal way, where for every effect there was a cause, neatly lined up in an orderly history. No anomalies, no miracles. But the fresh universes these creatures have selected are less optimal. They have rough edges. Effects preceding causes. Effects with no cause. Trailing threads. Threads to be picked out by the likes of me … You might even find gross violations, I suppose. Absurdities. For example, a universe where Julius Caesar never lived – but where a mass of evidence, documents and monuments, happened to be found that described his non-existent career. Effects without cause.’

‘And we found some of those threads,’ Stef said. ‘So did Ari, with his remains of the Drowned Culture. And Inguill with her mission patch from a flight to Mars that never happened.’

‘But all of this is an irrelevance, to the Dreamers. All they care about are the Hatches we build for them. And in each new reality we follow a cultural and historic logic that, yes, enables us to reach the stage of building Hatches ever earlier.

‘And so in each successive draft of cosmic history the Dreamers’ network of interconnectivity and communication reaches back, deeper into time, deeper into the past. The number of thoughts they are able to share grows, and their apprehension of the universe grows deeper. The Dreamers are essentially contemplative. If the universe is to be brief in duration – well, it is beautiful nonetheless, and deserves to be apprehended to the full. To be appreciated, to be studied and cherished, from beginning to end.’

‘It is monstrous,’ the ColU said. ‘It is magnificent. As if the universe itself, a finite block in space and time, is a kind of garden. A garden of which every square centimetre is to be tended, made as beautiful as possible, all the way to the back wall, so to speak. I am a gardener, or was; I can see the appeal of a cultivated cosmos. And all of it contained by the walls of birth and death.’

‘But the price of all this is raggedness,’ Stef said, dissatisfied on a profound level. ‘A universe of holes and patches, where scientific enquiry doesn’t necessarily make sense. And how far would they go to get to build their empire of the Hatches? Maybe in some realities mankind was eliminated altogether, and replaced by some other clever creature. Rats, maybe. Smart rodents burrowing through the multiverse like it was some roomy loft …’

Earthshine said, ‘And all of it, tidy or otherwise, doomed to incineration when the End Time comes. You see it now. We never mattered. We really are just a kind of technology to the Dreamers – created by their uplift programmes and then modified for a purpose. In fact I suspect the Dreamers don’t really believe we are intelligent at all. We are too small; there were always too many of us, getting in each other’s way. To them we are more like social creatures, industrious animals who blindly build things. Like ants or beavers.’

‘Or builders,’ Beth said.

‘Or road-laying legionaries,’ Titus said. ‘And given some of the lads I’ve worked with in my time, they might have a point.’

One morning Beth came to find Stef. She was grinning widely. ‘There’s something you need to see. As one veteran Per Arduan to another.’

She led Stef over to the ColU’s small Arduan garden. The ColU itself sat on a chair by the garden, roughly made by Chu from Arduan tree stems. ‘Colonel Kalinski,’ it said. ‘Look what I did.’

Beth took Stef to the edge of the worked soil. Reed-like stems grew in the earth in the shadow of the dwarf stromatolite, and in a shallow, marshy puddle.

Beth said, ‘Remember scenery like this? The ColU says it believes that the stems we see today are descendants of those of our time, of the first colonies. And it was those stems that bundled up to make builders. The ColU thinks the genetic potential to create builders is still in there somewhere; all he needs to do is cross-breed enough samples to restore the native stock.’

Stef thought that over. ‘You won’t have time, ColU. There are only months left—’

‘I know, Stef Kalinski. But you’ll forgive me for trying even so …’

‘I asked the ColU to do this,’ Beth said. ‘The builders saved my life, and my parents’, when we migrated with their lake – even if they didn’t know it. I always felt guilty about how the builders kind of got shoved aside when humans came pouring through the Hatch to Per Ardua. I wanted us to at least try.’

‘The ColU hasn’t succeeded, though, has it?’

‘No, but it’s made some progress. Come and see. Take a closer look. Just don’t get freaked out the way my father always said he was, when he first discovered these things …’

Curiosity pricking, Stef stepped forward to the edge of the pond and bent to see. The artificial pond was shallow, and its base was covered with mud, thick with lichen, from which the stems were growing. The stems themselves came up to her waist. They were an unusual kind, darker, flatter, more like blades than the usual tube-like structures, yet still substantial, still no doubt filled with marrow.

She crept closer, right to the water’s edge.

And on every stem, facing her, growing from the muddy pond scum, a single eye opened.

Earthshine said, ‘It was you, Stef, who first brought the Dreamers to my attention, in a sense. At least, their history-meddling. For your personal history was tinkered with in a minor way when you first opened that Hatch we found on Mercury—’

‘And suddenly I had a sister I didn’t remember. Suddenly my memory didn’t fit the facts of the universe as it existed.’

‘In retrospect, that was a classic loose end. An effect with no cause, in a universe that was now non-perfect, its causality become ragged. Or rather, more ragged.’

‘And later you found another loose end. The grave of my mother—’

‘Which still recorded she’d only had one daughter. Even as the second daughter stood there looking at the stone. And later, as you know – now I knew what to look for – I found more evidence of meddling. More evidence of lost timelines.’

‘The Drowned Culture.’

‘From these traces I deduced the existence of the Dreamers. Oh, not their nature, the fact that they were ensconced in the hearts of the rocky worlds. That came later. But I knew they were there, meddling, tinkering … In my fancy, I identified them with Loki, the trickster god of the Norse. Well, in the myth, Loki’s actions brought on Ragnarok, the final war – and in the course of that war another god, Heimdall, finally killed Loki himself. Was that to be my role? That was what I began to believe.’

‘And you did try to kill them,’ Stef said. ‘Or at least you made a start. You used Ceres to hammer Mars. Even much of the subsurface life, the Dreamers, must have been destroyed in that action. But what were you thinking? Would you have roamed the galaxy smashing one world after the next, trying to eradicate bugs hidden kilometres deep?’