Cana evidently read her expression. ‘So at last we’ve dug far enough into Luru Parz to find a conscience. At last we’ve found something that shocks you. And you’re wondering why any human being would cooperate with such monstrosity. I’ll tell you why. The alternative is worse. The alternative is the destruction of the species - an option the Qax have considered, believe me. That is why we are here, we who collaborate. That is what we must work ceaselessly to avoid.’

She stood, restless, and picked a slate off the wall. ‘Look at this. It is data on the deletion of data: a recursive register of destruction. And when all the primary information is gone, of course, we will have to delete this too. We must even forget that we forgot. And then forget that in turn. It will go on, Luru, a hierarchy of deletion and destruction, until - on one last data slate in an anonymous office like this - there will remain a single datum, the final trace of the huge historic exercise. If it falls to me I will erase that last record, gladly. And then there will be no trace left at all - except in my heart. And,’ she added softly, ‘yours.’

Luru, half understanding, was filled with fear and longing.

Cana eyed her. ‘I think you’re ready. You face a choice, Luru Parz.’ She reached into her desk and produced a translucent tablet the size of a thumbnail. ‘This comes from the Qax themselves. They are able to manipulate biochemical structures at the molecular level - did you know that? It was their, um, competitive edge when they first moved off their home planet. And this is the fruit of their study of mankind. Do you know what it is?’

Luru knew. The tablet was the removal of death.

Cana set the tablet on the desk. ‘Take it.’

Luru said, ‘So it is true. You have been bought with life.’

Cana sat, her face crumpling into sadness; for an instant Luru had the impression of very great age indeed. ‘Suddenly you have grown a moral sense. Suddenly you believe you can judge me. Do you imagine I want this? Should I have followed the others to Callisto, and hidden there?’

Luru frowned. ‘Where? Jupiter’s moon?’

Cana regained the control she had momentarily lost. ‘You judge, but you still don’t understand, do you? There is a purpose to what we do, Luru. With endless life comes endless remembering.