‘No more than all the women,’ Clara insisted. ‘If I can promise myself to a child, how am I a woman? If my flesh can become that child, how am I a man?’

Eusebio looked sickened, but he fought to maintain decorum. ‘These are your choices,’ he said. ‘If we’re to accept your help, we should respect your culture.’

Valeria buzzed. ‘Could I be the father of my own child – and live to see her do the same?’

Clara said, ‘Yes.’

‘But what about my co?’

‘Between you, you’ll have to decide. He could be the father of your child, if you both wanted that.’

‘And I could still live? He could trigger me, and I could survive?’

‘Yes.’

Valeria looked down at the speck of light that had been her city. ‘Who did all these things? We have to know their stories.’

‘You will,’ Clara promised. ‘We had some good archivists, but I think the translations will need to be a collaborative project.’

‘How many generations was the voyage?’ Eusebio asked.

‘About a dozen.’

‘A dozen,’ he repeated. ‘An era.’

All of this had grown out of Eusebio’s endeavours – and in one year from the launch, not four. Valeria thought it must feel as if he’d stepped out of his house for a day and returned to find his children replaced by a whole vast swarm of descendants, all of them with strange ideas of their own.

Valeria said, ‘And how many people lived and died in the mountain, without seeing the end?’

Clara squeezed her shoulder. ‘A lot.’

Valeria pictured them, generation after generation, lined up across the years. Farmers and physicists, inventors and instrument builders, maintenance workers, millers and cleaners, biologists and astronomers. Hidden behind her outstretched thumb, for ever out of reach. ‘I wish I could talk to them,’ she said. ‘I wish I could thank them. I wish I could tell them that it wasn’t for nothing, that it ended well.’

Clara said, ‘If that’s what you want, then I believe you’ll find a way.’

Appendix 1:

Units and measurements

Appendix 2:

Light and colours