‘I’m a physicist,’ Stef said, faintly baffled. ‘Not a biologist. A hell of a long time, I’m guessing.’

Beth said, ‘A lot more than the few decades since humans first got here – the few decades I remember anyhow.’

Stef said slowly, ‘In previous jumps through the Hatches – previous jonbar hinges – we jumped from location to location, maybe reality to reality, but without a jump in time. Correct? That’s aside from lightspeed delays. If you took the Hatch from Mercury to Per Ardua it was like a teleport from world to world, with a signal taking four light years to get to its destination – so you’d emerge four years later.’

‘And when we passed through the jonbar hinges,’ the ColU said, ‘save for lightspeed delays as you say, as near as I could determine the calendars always synchronised. Given some common starting event like the founding of Rome we could always match our chronologies—’

‘Have we crossed through time, then?’ Mardina asked, a little wildly. ‘Is that what you’re saying? Are we off in some future? How far? What would happen if we tried to go back through the Hatch? And – why should it be this way?’

‘I have only tentative answers to those questions,’ the ColU said gently. ‘We must wait to learn more.’

‘OK,’ Beth said. ‘Then come and learn about this …’

She led them further away from her camp, down a slope towards the narrow, fast-flowing stream that provided her fresh water. Here, by the stream bank and in the water, stems grew more thickly.

Beth paddled out into water that lapped over her boots, and knelt to touch a broken stem, almost tenderly. ‘One reason I came back to the substellar to live is because Earth life seems to prosper best here. Well, the stuff I could see – I wasn’t searching for earthworms. And I needed that, of course, to survive, the food crops. But if you go further out there are stretches that could be the Ardua we used to know, Stef, ColU. Stem banks and Arduan forests and stromatolites. But there are no builders. Not a trace of them. No middens and dams … No kites. None of the complex forms we saw when I was growing up – hell, that helped us survive.’

‘No more Mister Sticks,’ said the ColU gently.

‘What happened to it all, ColU?’

Stef asked, ‘Could it have been another jonbar hinge? I was there when you were debriefed, remember, Beth. When you first came through the Hatch to Mercury. You’d seen evidence of a much higher civilisation constructed by the builders.’

‘Yes. We found a map, a parchment in a Hatch. A global canal network—’

‘None of which you saw evidence of on the ground, or which subsequent human exploration turned up. Wiped out by a hinge, maybe. Is it possible that’s happened again, ColU?’

‘Unlikely. We’ve seen that the jonbar hinges tend to redirect the destiny of an intelligent species, rather than eliminate it altogether.’

‘You mean,’ Beth said sourly, ‘they’re made into better Hatch builders. Just as happened with humans, whatever the cultural cost.’

‘Precisely. Of course it’s not a neat process. The builders we saw seemed to have fallen away from that capability, somewhere in their own past. But I think what we’re seeing here is not the product of a jonbar hinge but—’

‘The result of time,’ Stef said, looking around, beginning to understand. ‘And worlds too, the framework for life, change with time. I’m being slow here, slow to pick up your hints, ColU. I am, or was, a physicist – not an astrophysicist, but I ought to be able to think about huge spans in time, as they did.

‘With time – a lot of time – as dwarf stars like Proxima age, they settle down. Become more quiescent. Planets too lose their inner heat. Volcanism, tectonic shifts tend to seize up. Per Ardua was a pretty active place when we knew it, Beth, and Prox helped too by serving up star winters, flares. But now, it’s evidently much more peaceful. A quieter world under a quieter sky. And on a quiet world—’

‘You can live a quiet life,’ the ColU said. ‘Beth Eden Jones, a big brain is expensive, energetically. On a more static Per Ardua, such luxuries have long since been evolved out. They just weren’t needed any more, you see? Instead all you need to do is find a sunny rock, spread out your photosynthesising leaves, and bask for ever more.’

Beth stared around. ‘So that’s what became of the builders? If they devolved – broke back down to the stems they were made of – how long would that take?’

‘So,’ Stef said, ‘we come back to time again, ColU. And a hell of a lot of it, it seems.’

‘A clock is ticking,’ the ColU said now. ‘I saw this when I was able to study the universe, aboard the Malleus Jesu, in the gulf between the stars. Echoes in the sky, of past events and future.’

‘What clock?’ asked Stef, growing exasperated. ‘What events?’

‘Beth Eden Jones, you have done a fine job of survival here. But our mission is to do more than survive. We must find Earthshine – while we still have time to do so. And I can’t see the sky from here. Not in this permanent day. I must see the sky, I must …’

‘Why?’ Stef snapped.

‘Because that is my ticking clock.’

‘We’ll have to leave here, then,’ Beth said.

‘Yes. We need to follow Earthshine, we must make for the antistellar … We must cross the darkened face of the world. We’ll need to prepare – warm clothes, food. It will take some time – but we must do this as soon as we can. I will tell you more when I know for sure myself,’ the ColU said patiently. ‘But for now, let’s begin to plan. We have a long journey ahead … Come, Chu Yuen, if you please.’

As Chu turned to begin the walk back to Beth’s camp, Stef saw Mardina’s hand slip into his, and squeeze tightly.

CHAPTER 61

When Stef and the others returned to the camp, and began the discussion about leaving for the antistellar, Ari drew Inguill aside.

They walked away from the others, on the pretence of inspecting the latrine ditch they had been working on. When they were out of earshot, Ari plucked out his earpiece. ‘I can speak Latin,’ he said in that tongue. ‘Can you?’

‘A little.’ Inguill removed her own earpiece. ‘I studied it in the course of my historical surveys. And my grasp has been refreshed by my contact with your group.’

Ari took the earpieces and set them down some distance away. ‘Then let us communicate in that way. I would prefer not to have our conversation passed through Collius.’

She smiled. ‘I think I know why.’

He eyed her. ‘You and I are not like these others—’

‘ “These others”,’ she said drily, ‘include your daughter and her mother.’

He smiled back. ‘That’s a long story. Nevertheless. You and I see further than the rest. We would not have come on this astonishing journey across the reality sheaves otherwise. Indeed I was blocked, once, from progressing even faster, from following this Earthshine into mystery, through a Hatch on a different Mars. And now we are here, in this place, wherever it is—’

‘Wherever and whenever.’

‘We are not here to dig ditches.’

‘I agree with that,’ she said.

‘Or to grow potatoes, or build lean-tos. Or to wait around until my daughter and Clodia Valeria rip each other to pieces over the Xin boy.’

She laughed. ‘You noticed that too. Then why are we here, Ari Guthfrithson?’

‘Isn’t it obvious? We are fascinated by the jonbar hinges. Whole histories are being wiped away, as if by the wave of a hand. To have such power—’

‘You think that is what this Earthshine has gone to seek.’

‘Isn’t that obvious too?’ His eyes glittered. ‘Now my wife and the rest, goaded by the ColU, are considering an expedition. We will all march off into the dark and the cold. But first we will grow more root vegetables, so that we won’t be hungry. Even then we will move at the pace of the slowest of the group. And all the time we will be in the control of the ColU—’