I'm almost sure that the first leap was made here, at this point the way I remember it now, there was a pause, an ominous silence, at the other end of the line. See? See? It can't be done, you'd think, not from here. Me: 'I just phoned to say that you've got to write a note for Molly to take in to school tomorrow. Molly's here watching TV, Tom's round at Jamie's.' I can remember the beginning of it, almost word for word: I keep missing the link, the point where it turned from a relatively harmonious and genuinely banal chat about minor domestic arrangements into this cataclysmic, end-of-the-world-as-we-know-it moment.

If my thoughts about our marriage had been turned into a film, the critics would say that it was all padding, no plot, and that it could be summarized thus: two people meet, fall in love, have kids, start arguing, get fat and grumpy (him) and bored, desperate and grumpy (her), and split up. To tell you the truth, the second part of this self-reflection only takes so long because twenty-four years is a long time, and there are loads of bits that come unbidden into your head, little narrative details, that don't really have much to do with the story.

Which turns into an endless, three-in-the-morning brood about how we'd got from there (meeting at a college dance in 1976) to here (imminent divorce) in twenty-four years. Later, in the hotel room, when I can't sleep - and that is some sort of consolation, because even though I have turned into the woman who ends marriages in a car park, at least I have the decency to toss and turn afterward - I retrace the conversation in my head, in as much detail as I can manage, trying to work out how we'd got from there (Molly's dental appointment) to here (imminent divorce) in three minutes. Sometimes we have to be judged by our one-offs. If you choose to conduct yours on a mobile phone, in a Leeds car park, then you cannot really claim that it is unrepresentative, in the same way that Lee Harvey Oswald couldn't really claim that shooting presidents wasn't like him at all.

But for the majority of people, marriage-ending conversations happen only once, if at all. I can describe myself as the kind of person who doesn't forget names, for example, because I have remembered names thousands of times and forgotten them only once or twice. That particular self-assessment will now have to be revised, clearly. Even though I am, apparently, and to my immense surprise, the kind of person who tells her husband that she doesn't want to be married to him anymore, I really didn't think that I was the kind of person to say so in a car park, on a mobile phone. He's at home, looking after the kids, and I have only called him to remind him that he should write a note for Molly's class teacher.

David isn't even in the car park with me. I am in a car park in Leeds when I tell my husband I don't want to be married to him anymore.

How to be good by nick hornby