‘You mean,’ Yuri said, ‘these little guys are feeding.’

‘I’ve observed the adults, too, spending time on lichen beds like this. But the youngsters are presumably more in need of nutrients; their stems need to grow. So the youngsters spend more of their time plugged in, so to speak. Other Arduan creatures, like the kites, must have similar rooting sites. If we look hard enough we’ll find them. Certainly these creatures, which are a mixed-up compound of what we call animals and plants, are never more plant-like than at such moments. Perhaps their animal-like consciousness, a sense of self-awareness and identity, briefly dissolves into a deeper green . . .’

Mardina wasn’t listening, Yuri saw. All her attention was on the young builders.

He said to her, ‘You like these little guys, don’t you?’

She looked defensive. He knew she didn’t like having her feelings questioned, any more than he did himself. But she admitted, ‘Look, I’m no noble savage. But I grew up with the old stories – you know? Of the gengas, the spirits of my ancestors infusing the land. Well, I have no ancestors here, there are no gengas for me. But these builders – this is their world. They honour their dead, we know that. Maybe their gengas will look after me. I know it makes no sense—’

The ColU said, ‘Careful.’

There was a clatter, like a bag of chopsticks being shaken. Yuri, standing over Mardina and the infants, turned to see a pair of older builders bearing down on them, spinning, limb stems clattering.

‘Hey, take it easy, you guys.’ Mardina stood up. She whirled around in her orange jumpsuit, shaking out her arms and legs. ‘We’re just looking, we won’t harm these little fellas.’

The ColU abruptly rolled back a half-metre, a sure sign in Yuri’s experience that it was surprised, and raised its sensor pod on its arm high in the air. ‘Lieutenant . . . what are you doing?’

‘What does it look like? Can’t you see these blokes are warning us off?’

Yuri said, ‘You mean they’re talking to us? What, with the dance?’

‘In the dance, in the way they clatter their limbs – I don’t know, I don’t speak builder. I’m just trying to reassure them, that’s all.’

The builders slowed their spinning and backed off a little, but they did not root in the lichen bed with the infants. Instead they stood at the edge of the bed, spinning slowly, evidently watching warily. Yuri thought he saw a glimmer of opening eyes, eerily human, eye-leaves hidden in their structures.

‘ “I don’t speak builder,” ’ the ColU repeated. ‘Yet, in a sense, you clearly do, Lieutenant. Fascinating. I must explore this further.’ And then it froze, camera-eyes staring at the builders, sensor pod held high.

Mardina picked up her pack. ‘Come on. The ColU will be stuck here for hours, observing away. You know how it is when it gets into this kind of mood. Let’s get out of here. We ought to stop spooking the builders.’

‘All right.’ Yuri hefted his own pack.

They walked on in silence, back around the southern shore of the lake, leaving the ColU behind. They kept well clear of the stems, the builder beds, the dome-shaped nest-shelters.

Builders moved everywhere, bent on their mysterious errands, working on peculiar, unidentifiable structures, sometimes even dipping into the lake water. In there, Yuri had learned, underwater creatures swam, more multi-stem forms, perhaps analogues of crabs or fish or crocodiles.

And at the water’s edge the builders came together in pairs, triples, larger groups, and they spun and clattered and buzzed around each other. Yuri had seen this kind of behaviour before, but had never thought much about it. Some failure of his own imagination. Yes, he thought, it was as if they were talking to each other. He wondered if it would ever be possible to translate what they were saying. If it was possible, he supposed, the ColU would figure it out.

They passed a garden of stromatolites, big ones, with broad cap-like upper surfaces over stout pillars, like huge mushrooms gleaming gold in the Prox light. A herd of herbivores worked the garden, small critters this time, no taller than the average builder, but they had the usual spiky extrusions, that they pushed into the rich interiors of the stromatolites. The stromatolites were so huge it was hard to believe they would even notice this pinprick feeding.

Then they came to a group of middens, standing by the southern lake shore. These were big heaps, with steep sides of compacted, dried-out old stems. Yuri saw builders working on their upper surfaces, a good number of them, pushing heaps of stems back and forth with an endless, dry, rustling sound.

‘They’re rebuilding the midden,’ he observed to Mardina.

‘Again. And the middens already have complex shapes.’ She had a slate; she sketched the nearest midden’s new layout with brisk, confident movements of her hand. ‘Look at it, Yuri. Think of it as a building, a structure. Forget that it’s a heap of old stems, of dead builders. Suppose it was made of concrete . . .’

It was a complicated design, of curves and banks and channels. And it was only one of a series of these middens, all along this part of the lake shore. Yuri turned, trying to figure out how these structures fit into the landscape. Away from the lake to the south, behind them, passing east of the stromatolite garden, he made out a shallow, rubble-strewn channel, a dried-up river bed maybe, leading to a depression, crusted with salt. The row of middens neatly sealed off this outflow channel from the lake.

‘It’s like a dam. I’ve thought that before.’

‘Hmm,’ Mardina said dismissively. ‘Maybe. Blocking that dry channel to the south. But there are what look like functional dams on the other side of the lake, the north shore. Blocking the inlet streams coming down from the high land between the lake and the forest. What do you make of that?’

He shrugged. ‘What is there to make of it?’

She squinted at the builders. ‘Depends how smart you think those little guys are. We know they build shelters for their young, we know they communicate between themselves, we know they remember their dead. Does all this building work going on around the lake have a purpose? However smart they are, they’re certainly smart in a different way from us, and that makes them hard to understand. Maybe we think they’re working on some big engineering project here just because that’s what we’d do.’

As they spoke Yuri saw the builders’ behaviour was changing. They had given up their work on the midden and were streaming down its flanks, heading towards the stromatolite garden. And in the nursery areas to the west, he saw adult builders gently shepherding the young towards the nest-like shelters.

Mardina pointed. ‘Here comes the ColU.’

The ColU was built for stability and strength, not speed. Still, it kicked up a cloud of dust as it raced around the lake towards them. And it called to them, its voice an over-amplified bark: ‘Danger, Yuri Eden, Lieutenant Mardina Jones, danger!’ It pointed up at Proxima with one extended manipulator arm. ‘Flare alert! Flare!’

Yuri turned and looked up at the star, shielding his eyes, squinting. He saw bright flare sites coalescing, and tremendous crackles like lightning flickering over the star’s sprawling surface. No wonder the builders were fleeing.

‘Shit,’ said Mardina. ‘That’s a big one, and it’s come out of nowhere. And we’re a long way from the storm shelter.’

‘I’ve got an idea.’

‘What?’

He pointed south-west. Most of the builders from the lake were streaming that way, spinning and pivoting, kicking up dust, heading straight for the big stromatolites. ‘Follow the builders. Come on!’

He led the way. When he glanced back to check that Mardina was following him, behind her he saw a flickering on the northern horizon. In the big trees of the forest, the huge triple canopy leaves were folding up like umbrellas.