‘Yes. How does matter know what to do, if it has never done it before? By probing such questions we explore the boundaries of reality.’

She stopped, breathing hard, and gazed up at the hovering ghost. ‘Is that all you do, this physics stuff? Do you have a family?’

‘That is . . . complicated. More yes than no. Do you?’

‘We have cadres. I met my parents before I left home. They were there at my Naming, too, but I don’t remember that. Do you have music?’

‘More yes than no. We have other arts. Tell me why you are here.’

She frowned. ‘We have a right to be here.’ She waved an arm over the sky. ‘Some day humans are going to reach every star in the sky, and live there.’

‘Why?’

‘Because if we don’t, somebody else will.’

‘Is that all you do?’ the ghost asked. ‘Fly to the stars and build cities and compete?’

‘No. We have music and poetry and other stuff.’ Defensively, she plodded on through deepening snow. ‘Soon we’ll change this world. We’re going to terraform it.’ She had to explain what that meant. ‘It will be a heroic project. It will require hard work, ingenuity and perseverance. Also we have brought creatures with us that are used to the cold. We found them on an ice moon a long way from our sun, a place called Port Sol. They have liquid helium for blood. Now we farm them. They can live here, even before the terraforming.’

‘How remarkable. But there are already creatures living here.’

‘We’ll put them in cases,’ said Minda. ‘Or zoos.’

‘We, my kind, can live here, on this cold world, without making it warm.’

‘Then you’ll have to leave,’ she snapped.

She reached the outskirts of the city.

It was a gridwork of foundations and low walls, all of it half-buried under a blanket of rock-hard water ice and frozen air. The buildings and roads seemed to follow a pattern of interlocking hexagons, quite unlike the cramped, organic, circle-based design of modern Conurbations on Earth, or the rectangular layout of many older, pre-Qax human settlements.

As she walked along what might once have been a street, the pain in her hands and feet seemed to be metamorphosing to an ominous numbness.

The ghost seemed to notice this. ‘You continue to lose heat,’ it said. ‘Shivering is no longer enough to warm you. Now your body is drawing heat back from your extremities to your core. Your limbs are stiffening—’

‘Shut up,’ she hissed.

She found a waist-high fragment of wall protruding from the layers of ice. She brushed at it with her glove; loose snow fell away, revealing a surface of what looked like simple brick. But it crumbled at her touch, perhaps frost-shattered.