It was a minor inconsistency that any rational person would have interpreted as a simple, innocent error, which in fact it was. But Freyberg’s expression indicated disbelief and he immediately scribbled on a notepad. When Rachel brought the coffee, he gave her the note. I diagnosed paranoia and started to think about escape plans.

‘I need to use the bathroom,’ I said. I planned to phone Freyberg from the bathroom, so Rosie could escape while he took the call.

I walked towards the exit, but Freyberg blocked my path.

‘Use my private one,’ he said. ‘I insist.’

He led me through the back of his office, past Rachel to a door marked ‘Private’ and left me there. There was no way to exit without returning the way we had come. I took out my phone, called 411 – directory assistance – and they connected me to Rachel. I could hear the phone ring and Rachel answer. I kept my voice low.

‘I need to speak to Dr Freyberg,’ I said. ‘It’s an emergency.’ I explained that my wife was a patient of Dr Freyberg and that her lips had exploded. I hung up and texted Rosie: Exit now.

The bathroom was in need of Eva’s services. I managed to open the window, which had obviously not been used for a long time. We were four floors up, but there seemed to be plenty of handholds on the wall. I eased myself through the window and started climbing down, slowly, focusing on the task, hoping Rosie had escaped successfully. It had been a long time since I had practised rock climbing and the descent was not as simple as it first seemed. The wall was slippery from rain earlier in the day and my running shoes were not ideal for the task. At one point I slipped and only just managed to grasp a rough brick. I heard shouts from below.

When I finally reached the ground, I discovered that a small crowd had formed. Rosie was among them. She flung her arms around me. ‘Oh my God, Don, you could have killed yourself. It didn’t matter that much.’

‘The risk was minor. It was just important to ignore the height issue.’

We headed for the subway. Rosie was quite agitated. Freyberg had thought that she was some sort of private investigator, working on behalf of a dissatisfied patient. He was trying to have the security personnel detain her. Whether his position was legally defensible or not, we would have been in a difficult position.

‘I’m going to get changed,’ said Rosie. ‘Our last night in New York City. What do you want to do?’

My original schedule specified a steakhouse, but now that we were in the pattern of eating together, I would need to select a restaurant suitable for a sustainable-seafood-eating ‘vegetarian’.

‘We’ll work it out,’ she said. ‘Lots of options.’

It took me three minutes to change my shirt. I waited downstairs for Rosie for another six. Finally I went up to her room and knocked. There was a long wait. Then I heard her voice.

‘How long do you think it takes to have a shower?’

‘Three minutes, twenty seconds,’ I said, ‘unless I wash my hair, in which case it takes an extra minute and twelve seconds.’ The additional time was due primarily to the requirement that the conditioner remain in place for sixty seconds.

‘Hold on.’

Rosie opened the door wearing only a towel. Her hair was wet, and she looked extremely attractive. I forgot to keep my eyes directed towards her face.

‘Hey,’ she said. ‘No pendant.’ She was right. I couldn’t use the pendant excuse. But she didn’t give me a lecture on inappropriate behaviour. Instead, she smiled and stepped towards me. I wasn’t sure if she was going to take another step, or if I should. In the end, neither of us did. It was an awkward moment but I suspected we had both contributed to the problem.

‘You should have brought the ring,’ said Rosie.

For a moment, my brain interpreted ‘ring’ as ‘wedding ring’, and began constructing a completely incorrect scenario. Then I realised that she was referring to the spiked ring I had proposed as a means of obtaining Freyberg’s blood.

‘To come all this way and not get a sample.’

‘Fortunately, we have one.’

‘You got a sample? How?’

‘His bathroom. What a slob. He should get his prostate checked. The floor –’

‘Stop,’ said Rosie. ‘Too much information. But nice work.’

‘Very poor hygiene,’ I told her. ‘For a surgeon. A pseudo-surgeon. Incredible waste of surgical skill – inserting synthetic materials purely to alter appearance.’

‘Wait till you’re fifty-five and your partner’s forty-five and see if you say the same thing.’

‘You’re supposed to be a feminist,’ I said, though I was beginning to doubt it.

‘It doesn’t mean I want to be unattractive.’

‘Your appearance should be irrelevant to your partner’s assessment of you.’

‘Life is full of should-be’s,’ said Rosie. ‘You’re the geneticist. Everyone notices how people look. Even you.’

‘True. But I don’t allow it to affect my evaluation of them.’

I was on dangerous territory: the issue of Rosie’s attractiveness had got me into serious trouble on the night of the faculty ball. The statement was consistent with my beliefs about judging people and with how I would wish to be judged myself. But I had never had to apply these beliefs to someone standing opposite me in a hotel bedroom wearing only a towel. It dawned on me that I had not told the full truth.