‘I expect there’s a moral lesson in all this,’ Beth said drily.

Again Stef was left with more questions than answers. Yes, she could understand the evolution of a cooperative community like this. But how long had that evolution taken? Time – the great mystery of this new Per Ardua.

They cleaned off their knives, packed the mushy organic material back into the wounds they’d created, and – with one last silent apology from Stef to the mutilated stromatolite – they returned to their riverside camp.

Ninety days out from the substellar, their faithful river at last flowed into a broader body of water, a lake perhaps, maybe even a sea. It was wide, stretching beyond their horizon, and choked with green life.

They decided not to try to cross it in the boat. So they camped on shore for a couple of days while reassembling their boat into a cart, and began the process of hauling their way around the lake, hoping to find a way to continue south-east, following their great circle. The haulers grumbled, and Titus chided them for their lack of fitness after so many days on the river.

After a couple of days they came to what appeared to be a broad isthmus, a neck of land separating their own lake and a neighbour that looked even more extensive. The isthmus led to what appeared to be higher ground to the south-east, densely carpeted with forest.

With relief that they were able to resume their course, they continued across this natural bridge. Titus strode boldly at their head, hauling on his harness with the vigour of a man half his age, Stef thought. He was magnificent in this setting, with the light of the slowly descending Proxima glimmering on the water around him, and casting an ever lengthening shadow ahead: he was the last of the Romans, pursuing one last impossible mission. Not that she was about to tell him so.

They reached the bank of forest at the far side of the isthmus. Compared to the substellar forest this was sparse, patchy – but, in the long shadows, quite gloomy. Titus and Clodia spent a day scouting out a likely route, and settled on another water course, heading south from the isthmus and cutting a track through the forest.

On they marched. As Proxima lost ever more height in the sky, so the nature of the vegetation around them changed again. The trees grew taller now, with big flaring leaves that strained to the north-west towards the lowering star, and at their feet the gathering shadows were broken by a greenish glow, reflections from the huge sprawling triple leaves. In some of these pools of illumination they found termite mounds, familiar from Earth, feeding off the reflected light of another star: another cute example of the cooperation of interstellar life in this strange environment.

They reached yet another milestone: a hundred and twenty days since leaving the substellar camp. When Stef looked back she saw that the disc of Proxima, dimmed and bloated by refraction in the thickening air, now touched the horizon. And when she looked ahead she could see splashes of light, islands in the sky. She remembered this from her last jaunt across the terminator, with Yuri Eden and Liu Tao, long ago. She was seeing the light of Proxima catching the peaks of mountains, while their bases were in permanent night, the shadow of the planet.

That was when Mardina announced she was pregnant.

CHAPTER 65

They built a camp in a valley of twilight.

They had walked into the shadow of the world, Stef realised. The sky, laden with thick cloud, was pitch-black. The only light they had, save for their own torches, came from the mountain that loomed over this valley, worn by time but still so tall that its summit and higher flanks were splashed by sunlight, and some of that daylight reflected into the valley below. Stef suspected they had stalled in this last scrap of light, before penetrating the interminable dark ahead, for reasons of instinct as much as logic; they couldn’t bear to leave the unending Proxima day behind.

Titus Valerius, as always, took charge. First he had them build a camp on a rocky outcrop rising from the generally muddy ground – and it always would be muddy here at the terminator, the ColU had warned, when it wasn’t snowing or icebound. It always rained at the terminator. As warm air from the day side spilled over into the chill of endless night, it dumped its moisture, and the ground everywhere would be waterlogged. But at least on this rock they could build a fire, and sleep out of the damp, and keep any rain off with their tent canopy supported by a frame of stem-tree trunks.

Then, once they were established, Titus gathered them in the glow of the fire. In the deepening cold they were already wearing extra layers of clothing, stuffed with padding; they all looked fat and clumsy.

‘We’ve done well so far,’ Titus said. As he spoke he ladled out a stew of potatoes and cabbage. ‘Mostly thanks to the rivers. A hundred and twenty days to these shadow lands, faster than I anticipated. But we’ve still got the same distance to cross again, and in the dark and the cold all the way, as I understand it. Yes?’ He looked around at them sombrely. ‘Some of you know this world; I was never here before. Sitting here I find myself uncertain about whether this mission will even be possible, the six of us dragging a cart through the dark for thousands of miles. Well, we must do the best we can. Just as we planned, we will now consider our situation, and prepare for the adventure ahead.’

Stef smiled at his choice of words. Adventure, not ordeal. The man was a natural leader. Looking around the group, she saw that he held everyone’s attention – everyone save Mardina, perhaps, who seemed unable to eat the cabbage, and was folded over on herself, her knees drawn up to her chest.

‘There are six of us, plus the ColU,’ Titus said now. ‘Four of you, all save myself and Clodia, will make one last effort to gather supplies. Clearly nothing will grow on the ice of the dark side, I understand that, so you must gather what you can from the nearside vegetation that grows in the sunlit areas a little way back, or even on the illuminated peak above us. By the time we leave our cart must be full, our packs bulging. Perhaps we can find a way to reduce more of the food, to boil it, compress it. If the challenge is too much we can do this more gradually, setting up a series of caches, pushing deeper into the cold step by step.’

Stef put in, ‘At least we’ll have no trouble with warmth, thanks to the Romans’ kernel oven. There will be no trees growing on the farside ice, no fuel for fires.’

‘True,’ Titus said.

Beth said, ‘So while we’re foraging and boiling potatoes, you and Clodia—’

‘We will be scouting,’ Titus said with a grin. ‘We’ll go exploring into the dark, a little way at least. Looking for a route forward. And looking for a way to shorten this trip.’

Beth frowned. ‘How would that be possible?’

‘I’ve no idea. But then I’ve never been here before.’ He glanced at the ColU, which sat on a folded-up blanket. ‘And, in a sense, neither have any of you, since – if I understand your hints correctly – somehow a great span of time separates this world from the one you knew before. Who knows what might have happened in all that time? Perhaps Per Ardua had its own Romans who left behind a road, straight and true as an arrow, leading us straight to the antistellar.’

Stef smiled. ‘I suppose it’s worth a look.’

Now Titus turned to Clodia. ‘And I will have you at my side, child, because you will be a valuable companion on such a mission. I’ve seen enough on this journey already to know that.’

‘Thanks,’ Clodia said flatly.

Titus looked at Mardina. ‘The alternative is for you to stay here and assist Mardina. You may imagine how much I know about pregnancies. Perhaps it would help Mardina to have another young woman at her side.’