The novel opens with its protagonist and narrator, Tony Webster, recalling fragmented images that have returned to him. A shiny inner wrist, a hot pan steaming in a sink, ejaculate being washed down a drain, a river rushing backward.
Tony, a sixty-year-old retired arts administrator who lives in London, goes back in his memory to the early 1960s. Tony is still in high school, where he has a close group of three friends. Adrian Finn is the cleverest of the group, answering teachers' questions with complex philosophical arguments. When a boy in their class hangs himself because a girl he slept with gets pregnant, they spend hours discussing the philosophical issues around knowing exactly what happened when everything they know about the death comes from rumors.
After graduating, Adrian moves on to Cambridge University, one of the top two universities in England. Tony goes to Bristol and starts dating seriously for the first time. Soon his girlfriend, Veronica, asks him to spend the weekend with her at her family's home. Tony is uncomfortable with the way he perceives he is being looked down upon as lower class. One morning he goes downstairs and finds that he and Veronica's mother, Sarah, are the only ones still at home. She warns him, in a cryptic statement, not to let Veronica get away with too much. She won't elaborate, and laughs as she throws the hot egg pan in the sink.
Tony and Veronica break up, only to sleep together for the first time shortly afterward. Veronica is angry when Tony doesn't want to keep seeing her, and they agree they cannot be friends. During their final year of college, Tony learns from Adrian that he and Veronica are now dating. Tony replies by saying he doesn't mind, but he dwells on the issue and sends a letter denouncing the couple and suggesting that Veronica is emotionally damaged because of some suspected abuse from her brother or father.
Several months later, Adrian commits suicide. He leaves behind a suicide note explaining that a person must end their life once they have concluded it is the rational thing to do. Tony cannot help but admire Adrian and how he has never veered from his philosophical beliefs, and yet he thinks it is a terrible waste.
In the present, Tony has married, had a child, divorced, retired, and now lives alone in a flat. Tony is confused to learn that Sarah Ford—Veronica's mother—has left him five hundred pounds in her will. She also leaves him a couple of documents, one of which is a letter in which Sarah says Adrian was happy in the last months of his life. The other is Adrian's diary, which Veronica refuses to hand over to Tony. He sends email upon email asking her to send it, but she only sends him one page: a cryptic calculation in which it seems Adrian is reasoning out the logic behind his suicide.
They meet on the Millennium Bridge in London and she gives him the letter he wrote to Adrian. In it, he suggested Veronica has emotional problems and Adrian should go on his own to ask her mother about what her "damage" is. When he reads the letter over again, Tony is struck by how immature and cruel it is; clearly he was jealous of their relationship and wanted to hurt the couple. He still wants to see the rest of the diary, though, and eventually Veronica suggests they meet up. She drives him to see a group of developmentally disabled men being escorted on a walk by a caregiver. She gets out of the car while Tony waits in the passenger seat. The group all appear to know her well, and they call her Mary.
Tony cannot fathom the significance of the encounter, and Veronica chooses not to elaborate. Tony goes back to the area in North London several times over the next few weeks and eventually finds the group drinking in a pub. He tells one of the men he is a friend of Veronica's, which seems to upset him.
The man reminds Tony of Adrian, and he emails Veronica immediately to tell her he is sorry for never realizing that she and Adrian had a son together. He believes he understands now everything Veronica has been through. In an angry response, she tells him he doesn't understand, and he never did.
Tony is baffled and so goes back to the pub, this time meeting the care worker he saw with the men. The care worker reveals that the man is Veronica's brother, not her son. His mother, Sarah Ford, died a few months earlier and the man, who is called Adrian, has not been taking it well.
The novel ends with Tony finally piecing together what Adrian's cryptic calculation had been. Tony was a major part of that calculation, because if he hadn't sent his cruel letter denouncing the couple, Adrian never would have gone to speak with Sarah about "damage," and Adrian's affair with Sarah never would have started and she never would have gotten pregnant. In the end, Tony realizes his letter precipitated Adrian's suicide.
