Callum had done the SETI thing right from the start, running downloaded data packets through the software he installed on his desktop PC. They wanted at least two hours a week from their volunteers, but Callum was committed: he did way more than that. The world was still on dial-up then, and the shriek of the modem became, in Claire’s mind, the unimaginable blurt of an alien vocalisation.

‘What are the chances?’ she’d ask, excited. Usually he scowled, but once he said, ‘You don’t know about the Drake equation? The smallest possible number of communicating technological civilisations in the galaxy, the smallest possible number, is two.’

Electrified, she watched the screen for what seemed like hours, until the scrolling numbers, the unpleasing monochromatic display, drained the thrill out of her again.

‘I’m bored,’ she complained, putting her head on the desk. ‘There’s nothing to do. It just runs by itself. There isn’t even anything to see.’

‘Go away, then,’ Callum replied.

He did not mind boredom; he did not mind relegation to an observer’s, a donor’s, role. There was something noble in the ingloriousness of unrewarded, anonymous service. The achievements of the individual could not equal those of the masses, and mass achievements demanded this kind of sacrifice. He was scathing of any desire for distinction: he despised genius theory, notions of self-actualisation, or anything else that might delude a person into thinking they were special. He liked to shock her with this perspective. Their parents too. He liked to say things like, When you look at worms, do the worms have different faces? He ate whole apples, pips and all. Sometimes he even ate orange peel, the bitter pith a peculiar satisfaction.

These were harmless shocks; others were more obviously self-destructive. When Callum had been lurking at the top of his pay grade at the hospital for two years, he was offered a promotion – manager of his team – and turned it down. Her father told her that, his neck flaming with irritation. He said, ‘What the hell was he thinking?’

Her mother pretended to be shocked as well. She patted Callum on the arm, chastising him indulgently, saying things like, ‘Isn’t he stubborn?’