‘Anyway it’s definitely not Freyberg,’ said Rosie, interrupting my thinking.

‘Why not?’ Freyberg was the least likely, but certainly not impossible.

‘Green eyes. I should have thought of it at the time.’

She interpreted my expression correctly: disbelief.

‘Come on, you’re the geneticist. He’s got green eyes so he can’t be my father. I checked it on the internet.’

Amazing. She retains a professor of genetics, an alien of extraordinary abilities, to help find her father, she travels for a week spending almost every minute of the waking day with him, yet when she wants the answer to a question on genetics she goes to the internet.

‘Those models are simplifications.’

‘Don, my mother had blue eyes. I have brown eyes. My real father had to have brown eyes, right?’

‘Wrong,’ I said. ‘Highly likely but not certain. The genetics of eye colour are extremely complex. Green is possible. Also blue.’

‘A medical student – a doctor – would know that, wouldn’t she?’

Rosie was obviously referring to her mother. I thought it was probably not the right time to give Rosie a detailed account of the deficiencies in medical education.

I just said, ‘Highly unlikely. Gene used to teach genetics to medical students. That’s a typical Gene simplification.’

‘Fuck Gene,’ said Rosie. ‘I am so over Gene. Just test the napkin. It’s the one.’ But she sounded less sure.

‘What are you going to do when you find out?’

This question should have been asked earlier. Failure to raise it was another result of lack of planning but, now that I could picture Gene as the father, Rosie’s future actions became more relevant to me.

‘Funny you should ask,’ said Rosie. ‘I said it was about closure. But I think, subconsciously, I had this fantasy that my real father would come riding in and … deal with Phil.’

‘For failing to keep the Disneyland promise? It would surely be difficult to devise a suitable punishment after so much time.’

‘I said it was a fantasy,’ she said. ‘I saw him as some sort of hero. But now I know it’s one of three people, and I’ve met two of them. Isaac Esler: “We must not revisit the past lightly.” Max Freyberg: “I consider myself a restorer of self-esteem.” Wankers, both of them. Just weak guys who ran away.’

The lack of logic here was astounding. At most, one of them had deserted her.

‘Geoffrey Case …’ I began, thinking Rosie’s characterisation would not apply to him, but if Rosie knew about the manner of his death she might interpret it as a means of escaping his responsibilities.

‘I know, I know. But if it turns out to be someone else, some middle-aged guy who’s pretending to be something he isn’t, then time’s up, arsehole.’

‘You’re planning to expose him?’ I asked, horrified. Suddenly it struck me that I could be involved in causing great pain to someone, very possibly my best friend. To his whole family! Rosie’s mother had not wanted Rosie to know. Perhaps this was why. By default, Rosie’s mother knew more about human behaviour than I did.

‘Correct.’

‘But you’ll be inflicting pain. For no compensatory gain.’

‘I’ll feel better.’

‘Incorrect,’ I said. ‘Research shows that revenge adds to the distress of the victim –’

‘That’s my choice.’

There was the possibility that Rosie’s father was Geoffrey Case, in which case all three samples would test negative, and it would be too late for Rosie to wreak her revenge. I did not want to rely on that possibility.

I turned off the machine.

‘Stop,’ said Rosie. ‘I have a right to know.’

‘Not if it causes suffering.’

‘What about me?’ she said. ‘Don’t you care about me?’ She was becoming emotional. I felt very calm. Reason was in control again. My thoughts were straight.

‘I care about you enormously. So I can’t contribute to you doing something immoral.’

‘Don, if you don’t do the test, I’m never going to speak to you again. Ever.’

This information was painful to process, but rationally entirely predictable.

‘I’d assumed that was inevitable,’ I said. ‘The project will be complete, and you’ve indicated no further interest in the sexual aspect.’

‘So it’s my fault?’ said Rosie. ‘Of course it’s my fault. I’m not a fucking non-smoking teetotal chef with a PhD. I’m not organised.’

‘I’ve deleted the non-drinking requirement.’ I realised that she was referring to the Wife Project. But what was she saying? That she was evaluating herself according to the criteria of the Wife Project? Which meant –

‘You considered me as a partner?’

‘Sure,’ she said. ‘Except for the fact that you have no idea of social behaviour, your life’s ruled by a whiteboard and you’re incapable of feeling love – you’re perfect.’

She walked out, slamming the door behind her.

I turned the machine on. Without Rosie in the room, I could safely test the samples and then decide what to do with them. Then I heard the door open again. I turned around, expecting to see Rosie. Instead it was the Dean.

‘Working on your secret project, Professor Tillman?’