‘And yet you, through heroic efforts, have worked it out anyway.’

‘I’m just trying to explain, Yuri Eden.’

‘All right.’

‘Yes, I have seen traces of this event in the genes, and also in some fringe organisms that have survived on Per Ardua to this day. And – now this is the significant point, Yuri Eden – I have established that all this occurred some five hundred and forty-two million years ago. Do you see? Do you see?’

‘See what?’ Beth sat up now, rubbing her eyes. ‘I smelled smoke in my dreams. I thought the ColU was on fire!’

‘No, honey, it’s just the camp fire.’ Yuri didn’t see the ColU’s point at all, he couldn’t care less about such abstractions, and as the unit rolled into the camp the conversation was already fading from his mind. ‘Go find your Mom, sweetheart, and I’ll help the ColU get everything put away safely.’

CHAPTER 40

Mardina prepared lunch.

It was a kind of quick picnic assembled from chuno. This was a long-lasting paste you could make from potatoes by freezing, thawing, desiccating them – a smart trick from the Andes that the ColU had taught them, and invaluable for their travelling phases, but the result was a greyish muck in appearance that Beth had always cordially hated. But today she was hungry after the long journey back to the camp, and excited about the move. Certainly she didn’t want to sleep any more. They all had a peculiar mixture of tiredness and energy, Yuri thought, like they had gone on vacation maybe.

They decided to take the rest of the day off, and go exploring. The ColU, after trying to speak to Mardina about its mysterious science conclusions, grumpily rolled away and began the process of unpacking its last load from the old camp, including another tonne of terrestrial topsoil.

The family walked to the lake’s latest location, with Beth skipping ahead, and Mardina and Yuri side by side.

The ground in this country, away from the lake and the water courses, was as arid as they had ever experienced it. In fact, Yuri suspected the landscape was becoming drier, hotter, the further south they travelled. Which made sense; the further south you went and the closer to the substellar point you reached, the further Proxima rose in the sky, and the more heat it delivered. Yuri still had the map Lemmy had compiled from the colonists’ remembrances of the shuttle flight, before they’d all killed each other, and that showed concentric bands of climate and vegetation types around the substellar. If they walked far enough, Yuri supposed, they would in the end reach true lifeless desert, surrounding the substellar point itself, which the ColU predicted would be the site of a permanent storm system. Even before that, maybe there would come a point where the ground was no longer habitable for them at all. But they were following the builders, who had evidently been going through this process for uncounted millennia, and Yuri and Mardina had decided to trust them – well, having followed the jilla this far, they had no choice.

They came to the lake shore, a fringe of muddy ground with banks of new stems growing vigorously. The stems seemed to be self-seeding, but the colonists had observed the builders practising what looked like simple agriculture to help the stems along, planting shoots, irrigating the mud with crude drainage ditches. The water itself was still turbulent and turbid, not yet having settled into its new bowl. Around the shore of the lake Yuri could see builders working, setting up what looked like a nursery area with the outlines of domed shelters rising up from the debris – and already assembling basic middens, in preparation presumably for the next move of the jilla.

But there was another area where builders, adults and children, had been herded in a huddle, surrounded by others that spun and whirled around them. One by one the prisoners were taken out to an area where more builders pinned them down and, brutally, crudely, disarticulated them, taking away their constituent stems to one of the new midden heaps. It looked like a prison camp crossed with an open-air operating theatre – or, perhaps, like some appallingly brutal schoolyard game being played out by stick puppets. The sound of the continuing murders was an eerie rustling, a clatter of sticks, the scrape of sharpened stone on stem bark.

Yuri and Mardina gently guided Beth away from the scene. They had seen this many times before: it was the aftermath of a builder invasion, of conquest. There had been another community of builders here, living in the formerly dry lake bed, happily feeding off the local springs and stems – before the jilla folk arrived, brutally evicted them, flooded their homeland, and massacred any survivors.

Beth hadn’t yet worked this out. Now, luckily, she spotted the nursery and ran that way to see.

‘The same every time,’ Mardina said, looking back at the slaughter yard. ‘And I used to think the builders were cute . . .’

Yuri said, ‘They’re little wooden Nazis. Some day we’re going to have to explain all this to Beth, you know.’

‘Genocide in Toyland. There’s never going to be a good day to talk about that. Maybe you could tell her about your Heroic Generation at the same time. Give her some context. It’s not just builders that behave this way.’

‘For the thousandth time, it wasn’t my . . .’

But of course she was only goading him, for the thousandth time. She asked, ‘What did the ColU want to talk to me about, by the way? Seemed very intense.’

‘Oh, one of its theories. Life on Per Ardua. It seems to have got a pretty good family tree for this world now. Lots of bragging about genetic comparisons and stuff. He’s identified major revolutions in the story of life here.’

‘What revolutions?’

Yuri thought back. ‘Photosynthesis, I mean a fancy advanced kind that produced oxygen as a waste product. Then complex cells, with nuclei. Then plant and animal life. The ColU got worked up about the dates it’s established for these events. Meant nothing much to me.’

‘What dates?’

He concentrated. ‘Photosynthesis two point seven billion years ago. The complex cells two billion years ago. And the animals – umm, five hundred and forty-two million years ago, I think.’

Mardina stared at him.

Some distance away, at the fringe of the trodden mud around the new lake, Beth had found something worth shouting about. She jumped up and down, waving. ‘Mom! Dad! Come see!’

Mardina called, ‘OK, sweetie.’ They began to walk over. ‘Yuri – are you sure about those dates?’

He felt uncertain, now she pressed him. ‘Well, I think so.’

‘It’s just – I’m no expert, but I took terraforming modules during my ISF training, and we studied the history of Earth life, the key transitions. Yuri, the dates for the similar events on Earth are: two point seven billion years, two billion years, and—’

He guessed, ‘Five hundred and forty-two million?’

‘Yeah. I mean the last particularly is pretty precise, from the fossil record on Earth.’

‘Mom! Dad! Come see, before it all gets trampled!’

Mardina said, ‘Life on two worlds separated by light years having a common sugar base – well, you can wave your hands about panspermia to justify that. But such a precise coordination of the key dates of all those improbable events?’

‘What does it mean?’

‘Damned if I know.’

‘Mom! Dad!’ Beth, quite agitated, was almost screaming now.

And when Yuri and Mardina finally got there, at the edge of the pond’s muddy fringe, they could see immediately why.

Beth had found a human footprint.

CHAPTER 41

The invitation from Earthshine reached Stef at her workstation in the UN kernel lab on the moon.