Chu hung his head, Stef observed, as if he was still a slave who had been caught doing wrong.

‘But,’ Titus said heavily, ‘that doesn’t mean you’re lovers. Just because you sleep together. I mean, I remember once on campaign—’

Clodia growled, ‘Oh, Father.’

‘Well – whether or not, Mardina, I don’t see what your problem is with Clodia.’

Mardina flared. ‘You see us sleep together but you don’t see what she’s doing? The way she’s sitting beside him now. The way she looks at him. Leans against him. Holds onto his arm when the boat rocks—’

‘Don’t be absurd.’

‘Actually, Titus,’ Beth said with a rueful smile, ‘I noticed the same thing. I don’t think there’s any malice, though, Mardina. I don’t think she can help it. Look, girls, the problem isn’t with the two of you, or with Chu. It’s just that there’s only the three of you, three youngsters – in this boat, on this whole wretched planet. This problem was always going to come up.’

Mardina glared at her. ‘Oh, how helpful that is, Mother. So what do you suggest we do? Kill each other over Chu, the way those colonists did on Per Ardua like you’re always telling me?’

‘Ideally we will avoid that,’ Titus said with a dangerous calm. ‘But while you three work it out, here are the military rules. We’re on a mission here. And we also face a challenge to survive, as simple as that. You three can bed-hop as much as you like,’ and he kept his eyes averted from his daughter as he said it. ‘But if you come to blows, if I get a hint of a sniff of suspicion that you’re putting us all in danger – why, then, I’ll put a stop to the whole business. I’ll cut your pecker off, slave boy, and skin it and use it as a wind sock. Let’s see these young women fight over you then.’

Chu seemed to think that over. ‘It would be a big wind sock, sir—’

‘Shut up.’

For a time they progressed down the river in silence.

Then, from inside its waterproof wrapping, the ColU spoke up. ‘Well, this is awkward. Shall we sing a song? There’s one you may remember, Beth, from your childhood, with Yuri Eden and Mardina Jones – not that we had a boat in those days. Row, row, row your boat … Come, please join in …’

As they drifted on down the river its voice echoed from the life-choked water.

CHAPTER 64

With time the great waterway broadened and deepened, with many tributaries flowing into it from the surrounding land, just as Titus had predicted.

Then there came a day when ‘their’ river passed through a confluence and became a tributary of a much wider river still. Soon the flow was so wide that it was difficult to make out the far bank. ‘We’re in luck,’ Stef said. ‘We found the local Mississippi.’ But of her companions, only the ColU and Beth knew which river she meant, and even Beth, Arduan-born, wasn’t sure.

Titus insisted that they should stay close to the bank, fearing stronger currents in the middle of the channel – and, just possibly, more aggressive life forms than they’d yet encountered. Even so, they swept on with what felt like ever increasing speed.

Without the physical effort of the march – the hardest work was the daily labour of hauling the craft up the bank for the night – and with Proxima sinking almost imperceptibly slowly in the sky behind them, the days passed in ever more of a blur to Stef. Even so it was a surprise when the ColU announced, that they had already been travelling for sixty days.

The character of the landscape around the riverbanks was changing once more. Much of the vegetation was waist high, and Stef was reminded of the prairies of middle America – or rather, of museum reconstructions she’d seen of such ecologies as they’d been before the climate Jolts. With the air cooler and Proxima lower still, the ground-blanketing ‘lilies’ were no longer so successful, and plants that stood up and bore leaves tilted towards the star did better. There were even trees here, or tree-like structures, with big leaves competing for the life-giving light, some stubby and fern-like, some quite tall and rising above the ‘prairie flowers’. But in this more open country some terrestrial plants fared better too, and the travellers gratefully scooped up handfuls of wild potatoes, yams – even grapes from vines that grew laced over Arduan trees, a cooperation across the two spheres of life that the ColU said it found pleasing.

The ColU never asked for stops. It seemed too aware of the pressure on them all to make good progress, and to push on with the journey. But sometimes, during their ‘night’ stops, it would ask Chu, or perhaps Beth or Stef, to take it to sites of particular interest. Such as exposed rock formations – which were rare; this Arduan continent was worn as flat as the interior of Australia. And the ColU would ask for samples to be taken, for fossils to be sought.

‘You’ll remember, Beth Eden Jones, how frustrated I used to get! This planet was once so active, chunks of its surface forever churning up, that any fossils were destroyed, the very layers they had formed in disrupted – the whole fossil record was a mess. Now that the world is so much more quiescent there’s at least a chance of finding some kind of decent record, at least of comparatively recent life forms …’

But all it ever found were what looked to Stef like matted banks of reeds, compressed into the sandstone and petrified. If there was no significant change, no extinction or evolution, she supposed, you were going to get a featureless fossil record, no matter how well preserved. Nothing but stems for – how long? Millions of years?

What Stef did notice herself, and she discussed it with the ColU, was an utter lack of evidence of the works of humanity.

‘We know people were here, once, on this Per Ardua. Right? The potatoes and the grapevines wouldn’t be here otherwise. But where are their towns? Oh, the buildings would burn down and crumble away, but where are their foundations, and the waste dumps, and the outlines of farmers’ fields? Where are the remains of their roads and rail tracks? We were on the way to setting up farms and mines all the way to the terminator. But it’s all just as it was at the substellar – gone. How long would it take to erode all that to dust, ColU?’

But as always the ColU refused to speculate about time. ‘We will know soon enough,’ it said. ‘As soon as I see the dark-side sky. We will know how long then.’

Once the ColU asked to be taken into a stromatolite garden, where those complicated mounds of bacterial layers, each about chest high, were growing together in a close crowd.

‘Of all the Arduan life forms I have observed – save only the builders themselves – the stromatolite is perhaps the most characteristic,’ the ColU said happily from its pack on Chu’s back. ‘And the most enduring. Here before all the rest, probably, and still growing strong, even now in the end days.’

And Stef wondered, End days?

‘Yet,’ the ColU said now, ‘there seems to be something subtly different about these particular specimens. Beth, Chu, do you have knives?’

It had Beth slice open one of the stromatolites, through its carapace and thick trunk. Within was a greenish mush, vaguely stratified. Beth dug in with her hands, but yelped, ‘Ow!’, and pulled back quickly. ‘Something bit me …’

She called Chu and Stef over, and, more cautiously, they dismantled the slimy interior of the stromatolite, chunk by chunk.

Then they found the ants’ nest. Black bodies, big, each maybe a thumb-joint long, came swarming out in protest at the intrusion of daylight.

The ColU seemed thrilled. ‘How wonderful! More ecological integration, more cooperation. Perhaps the terrestrial insects feed off detritus trapped in the layers of the growing stromatolite. And the structure as a whole must benefit from the internal mixing-up by the insects. Two life forms originating on worlds light years apart, evolving ways to live and work together, for the benefit of all.’