Mardina, however, looked less out of place. They had both abandoned their ISF-issue outfits by now, and wore looser clothing mostly made from local materials. In her tunic and short-cut trousers, coolie hat and bark sandals, and with her skin coated with grey-orange Arduan dust, Mardina wore the shades of the planet. Humans had come here to colonise Per Ardua. But, Yuri thought, what was really happening was that Per Ardua was colonising the humans.

And what drew all three of them, including the ColU, away from the farm and deeper into the embrace of Per Ardua were the builders.

On another dull day, their chores done, on impulse Yuri and Mardina trekked out to the lake. It was midday, by their human clocks. The ColU was already out at the shore, pursuing its own interests.

Mardina had become fascinated by the builders’ big projects around the Puddle: the dams that obstructed the inflow streams from the higher ground to the north – dams established long enough now to have created extensive floods behind them – and the more mysterious middens on the southern shore, with their banks and arcs. She walked along the lake’s northern shore, capturing images on her slate and sketching maps and diagrams with a stylus. ‘We still have no idea what all this is for. But whatever the hell they’re doing here, it’s evidently a lot more interesting than us digging in a few potatoes. Does it ever strike you how incurious they’ve been about us recently?’

That was true. The builders around the lake, a few hundred individuals gathered in a dozen small bands, all seemed part of a single community. Once the group around the nursery area on the western shore had got used to the idea that these strange, lanky, stemless creatures and their big rolling box were harmless, the other bands had soon seemed to pick up the same message, and stopped reacting to them. Unless you stood right in front of one and somehow impeded its progress, the builders just ignored the humans, spinning around you as if you were of as little interest as a lump of rock.

‘I think they’re working up to something,’ Mardina said now. She sounded breathless, and she sat on a lump of rock, her slate on the ground beside her. It was another chilly day and she wore an old fleece jacket over her stem-bark tunic. ‘All this work, the dams and mounds. They run around like this all the time, but the activity seems to be getting more intense every time I come out here.’ She massaged her lower spine with both hands; backache had plagued her pregnancy.

‘Maybe.’ Yuri squatted on the ground beside her, dug a water bottle out of his flask and handed it to her.

She waved it away. ‘You go find the ColU. I’ll stay and watch a while. Wouldn’t want to miss the show, whatever they’re planning, if it all happens to kick off today.’

He stood. ‘You’re sure you’re OK?’

He knew what reaction he’d get for that, and he got it. ‘You’re worse than that bloody nursemaid on wheels. My brain is still functioning, more or less, thank you, so don’t fuss, ice boy. Just piss off and go and annoy the ColU.’

‘All right. You’ve got water, you’ve got—’

‘The flare pistol, yes, I’ve got it, and I’ll fire it up your defrosted arse if you don’t bugger – off.’

So he did.

He soon found the ColU.

The big machine had rolled up to one of its own favoured sites for builder-watching, which was the eastern shore. Here there was no intense construction activity, as there was at the north and south shores, and no nurseries as at the west. The builders were always busy here, but engaged on smaller-scale tasks. For instance they had built an elaborate series of traps out into the lake water, from which they extracted small fish-like creatures, with stem-based skeletons like the rest of the wildlife but wrapped in a skin-like streamlined webbing – a casing easily unwrapped, and the contents picked apart and incorporated into other bodies.

And the builders weren’t so busy that they could not be distracted by a dancing robot.

Of course the ColU couldn’t really dance; it was built more like a tank than a ballerina. But, given Mardina’s lead, it had become ingenious at simulating builder-dancing with the forest of manipulator arms that sprouted from its deck. Now, before an audience of three builders, all adults – of course there would be three, or nine, or twenty-seven of these creatures of three-fold groupings – the ColU put on a show. It held up heavy-duty arms to simulate the three main limbs of a builder, and while it couldn’t literally make its puppet-builder spin around, with a kind of sleight of hand, its smaller arms twisting and writhing, it made it look as if it was spinning, accompanied by the nods, rocks and gestures that characterised builder movements.

The builders were not watching passively. They spun and dipped in their turn, as if they were speaking to each other as well as to the ColU – as if it had been accepted into some kind of conversation.

One of them was injured, Yuri saw; it had a damaged leg stem, broken near the base, so that it hobbled, its spinning a little off-balance. And as Yuri approached, he sensed a strange, intense smell, a smell of the lake, the stems – the scent of builders, amplified and enhanced, a scent reproduced artificially by the ColU.

‘Welcome, Yuri Eden!’ the ColU called, continuing its puppet show.

Yuri kept back from the little group. ‘You look as if you’re actually talking to them.’

‘Indeed! I have made spectacular progress in the months since I was inspired by Lieutenant Jones’s intuitive grasp that the builders’ dancing is a kind of communication. I have begun to build up an extensive vocabulary of “words”, which—’

‘I didn’t know you’d got so far. You haven’t told us about any of this.’

It sounded faintly offended. ‘I was waiting to complete the project. Or at least bring it to the point where I could make a proper report.’

‘This isn’t an academy.’ That was one of Mardina’s choice lines. ‘Just tell me what you’ve learned.’

‘A lot – or perhaps only a little. You must appreciate the challenge. Humans share a universal grammar that derives from your body shape, the way you interact with your environment, your experience of birth, life, death. A builder’s experience – the way a creature that is half-animal, half-plant by terrestrial categories apprehends the world – really is quite alien, and therefore so is its language. Also builder communication has a whole range of components, the most important being the gestural – the dancing – and scent: they emit body chemicals at will. I get the sense that they are a very old species, Yuri, and their mode of communication is very ancient. I mean ancient in the biological sense. Much older than human languages. Indeed, it has surely evolved on biological timescales, rather than cultural. As a result their language is wideband, in a way, with many channels of discourse, most of which I suspect I have yet to discover.

‘So we started with the basics, with simple nouns for obvious concrete objects. “Lake” was the first, as you can imagine.’ Its arm-puppet gave a series of twirls, and Yuri smelled a sharper tang. The builder audience responded in kind. ‘But even for a simple concept like “lake”, the builder word is much more complex, with many meanings overlaid; it means something like “the interface between mother and father which brings life”. That is my perhaps clumsy interpretation. It is as if every time I use the word “lake” I give you its history in terms of a Latin root imported into English via Norman French, together with mythological footnotes—’

‘Mother and father, though?’

‘Ah, yes: to them Proxima is the father, in terms of emotional analogies with the human condition, and the world, Per Ardua, is the mother – or more specifically, I think, the term refers to the lichen-rich nutrient patches in which their young take root. The adults who actually nurture infants are referred to by a term I think translates as something more like “midwife” rather than “parent”. From such beginnings I have established many more common terms, for water, earth, sky, hot, cold, big, small—’