‘I don’t need your advice,’ she growled. But her breath was misting, and there were tiny frost patterns in the corners of her faceplate. The cold was sharp in her nose and mouth and eyes.

The ghost said, ‘Your body is a bag of liquid water. I surmise you come from a world of high ambient temperatures. I, however, come from a world of cold.’

‘Where?’

The hovering globe’s hide was featureless, but nevertheless she had the impression that it was spinning. ‘Towards the centre of the Galaxy.’ Something untranslatable. A distance? ‘And yours?’

She knew how to find the sun from here. Minda had travelled across a hundred and fifty light years, at the edge of the great colonising bubble called the Third Expansion, towards the brilliant young stars of Scorpio and the Southern Cross. Now those dazzling beacons were easily identifiable in the sky over her head, jewels thrown against the paler wash of the Galaxy centre. To find home, all she had to do was look the other way, back the way the great fleet of Spline ships had come. The sun, Earth and all the familiar planets were therefore somewhere beneath her feet, hidden by the bulk of this frozen rock.

She was never going to see Earth again, she thought suddenly, desolately; and because this ice-block world happened to be turned this way rather than that, she would never even see the dim, unremarkable patch of sky where Earth lay.

Without thinking, she found herself looking that way. She snapped her head up. ‘I mustn’t tell you.’

‘Ah. Competition?’

Was the ghost somehow mocking her? She said sharply, ‘If we have never met before, how come I understand you?’

‘Your vessel carries a translator box. The box understands both our languages. It is of Squeem design.’

Minda hadn’t even known her flitter was equipped with a translator box. ‘It’s a human design,’ she said.

‘No,’ the ghost said gently. ‘Squeem. We have never met before, but evidently the Squeem have met us both. Ironic. It is a strange example of inadvertent cooperation between three species: Squeem, your kind, mine.’

The Squeem were the first extra-solar species humanity had encountered. They were also the first to have occupied Sol system; the Qax, soon after, had been the second. Minda had grown up understanding that the universe was full of alien species hostile to humanity. She glanced around. Were there more silver ghosts out there, criss-crossing the silent plains, their perfect reflectiveness making them invisible to her untrained eye? She tried not to betray her fear.

She asked cautiously, ‘Are you alone?’

‘We have a large colony here.’ Again that odd hesitation. ‘But I, too, am stranded in this place. I came to investigate the city.’

‘And you were caught by the volcano?’