The Curator said dryly, ‘Perhaps you can see why many of us working in this place prefer to forgo personality. It’s better not to think about it. Better still not to be able to think . . .’

The stations were set out in orderly rows, a neat rectangular grid. Symat counted no more than twenty or twenty-five rows in each direction: there were only a few hundred Ascendents here.

The Curator seemed to know what he was thinking. ‘Four hundred and thirty-seven. If you’d come here a decade ago there were four hundred and thirty-eight.’

Mela asked, ‘This is all?’

‘As a group they have been ineradicable. They have time on their side: that’s what you always have to remember about Ascendents. If you try to get rid of them, no matter how strong you are, all they have to do is wait for you to grow old and die, and for your children and grandchildren to die too, wait until you’re nothing but a sliver of data in a history text, and then they just walk back in.’

‘They are dying out, though.’

The Curator shrugged. ‘Nobody is making immortals any more. And entropy catches up with us all in the end. But despite their strangeness, they are mankind’s treasures.’

Mela asked, ‘Why do you say that?’

‘For all they have seen,’ the Curator said. ‘For the wisdom they have accrued, when you can dig it out of them. And for all they have done for us - and continue to do. It was the undying who founded the Transcendence, who tried to bring us to a new plane of being altogether. They ultimately failed, but what a magnificent ambition!’

‘And you say they still work for us?’ Mela asked.

‘By moving Port Sol,’ Symat saw immediately.

‘Yes,’ the Curator said, ‘But what they have done is rather more spectacular than pushing around a mere ice moon! You see, long ago, the undying resolved to move the Earth itself . . .’

It was the sun, of course.

As the downpour of solar radiation grew too intense, Earth’s natural processes couldn’t be sustained. And when the swelling sun’s photosphere washed over it like a misty tide, would Earth be sterilised, scorched, melted, even vaporised? It would take a long time, hundreds of thousands of years, before Earth was destroyed entirely. But Ascendents fretted on long timescales. You could say that was the point of their existence.

How do you save a world from an overheating sun? Mankind had never had the power to tinker with the processes of stars themselves. Could you shield the world with mirrors and parasols lofted into space? But any such shield would eventually be overwhelmed as the sun expanded. There was only one option: to move the Earth itself. But how?