Joe Rose, scientific author and journalist, and our first-person narrator claims that the "beginning" of this story "is simple to mark". However, the following events appear anything but simple. Whilst enjoying a picnic with his long-term (seven years now) partner Clarissa Mellon, a literature academic and Keats scholar, a ballooning accident occurs - a catastrophe for virtually all those involved.
Immediately Joe runs to help the pilot, James Gadd and his son Harry as they fail to bring the balloon under control. Joe is joined by several other strapping men; Joseph Lacey and Toby Greene, farm labourers; John Logan, a fit doctor and the fateful Jed Parry. Winds lift the balloon up, only Harry is inside, he's young, he's urinating and he'll be in trouble if the others let go of the ropes holding the balloon down, which is what they do. Cue for much macho guilt re: who let go first, especially as John Logan doesn't let go at all and so floats up high till he can hold no longer and from a distance that's far too high he falls.
Joe feels important, "a kind of self-love", sees Jed Parry is in 'shock' and so decides to hold his gaze, including Jed in Joe's own "self-congratulatory warmth" at being alive. Bad move Joe. This is where his personal catastrophe may 'begin', simply or otherwise. Joe decides to visit Logan's body. It's dead, he feels sick, Jed joins him and suggests that "we could ... pray together?". Joe's a good atheist, he refuses despite Jed's persistence and slightly disturbing mixture of joy and pity at rejection. That night, Joe and Clarissa retell their stories, we learn that Clarissa is barren but has great "frustrated love" for children. They find sex a comfort then the phone rings. Jed tells Joe he loves him. Joe makes his "first serious mistake" as he tells Clarissa it's a wrong number.
Next day, Joe and Clarissa lose themselves in work. Joe thinks he's being followed at the library - or is he deluding himself? However, we learn Jed has rung the flat again. Joe unplugs the phone so he and Clarissa can enjoy each other's company.
The day after Joe tells Clarissa about Jed's call, she laughs at first but is not impressed when he mentions how he feels 'followed'. She leaves, Jed calls again, this time from the phone box at the end of Joe's road and reluctantly Joe agrees to meet. All Jed's whining words suggest Joe is hiding 'real' feelings for him, which he's pretending not to know about or is unconscious of. He accuses Joe of playing games with him. Joe gets into a cab, but not before Jed asks for a meeting between the three of them - Clarissa needs to know! On Joe's return Jed's outside the flat, waiting. He makes numerous calls to the answer-phone, so Joe rings the police but has no luck. We learn of Joe's dissatisfaction with his writing life, how he wants to get back into 'real' science.
Clarissa returns and we are told the story from her pointof view - she's had a bad day at work and Joe launches into Parry and getting back into science. She questions his claim re: the messages - Joe's wiped them - and is worried: is Parry real? Joe feels she doesn't believe him, there's an argument, he walks out to find it's raining hard and Jed is waiting for him. Joe is troubled by references Jed made to curtains, Jed catches up with the storming Joe who feels he wants Jed's death. Jed continues to make Joe the agent for all this and uses obscene, quite threatening language for the first time. Joe loses him.
We now get another perspective, a letter written by Jed, in which he refers to his 'mission' to love Joe and bring him to God. We learn of Jed's past and the kind of man he is. A couple of days after this first letter Joe drives to see Logan's widow. He's thinking of Clarissa's reaction to the letter - she thinks the writing is rather like Joe's, their relationship is destabilising. He searches her study for evidence of a possible affair to explain her 'indifference' to his plight but finds nothing. He decides he's seeing Mrs Logan to establish his guiltlessness. She is destroyed not just through grief but the certainty that her husband died because he was showing off - to the woman he was having a secret affair with! Mrs Logan wants Joe to find 'her'. He toys with her children over the concept of 'lying' and remembers why curtains were bothering him so - it reminds him of de Clerambault's syndrome: a framework of prediction for an infatuation such as Jed's.
When Joe returns home he discovers, via Jed, that he's paid a researcher to read all Joe's articles. What else could Jed pay to get done? Clarissa confronts Joe over searching her study, he made it so 'obvious' - what's he trying to tell her? We get another letter from Jed; he's saddened by Joe's 'dry thoughts' and there's a veiled threat. This leads into Joe and Clarissa admitting they've lost the 'trick of love'. Joe can't stop thinking about Jed, he's getting over three letters a week and is searching for concrete threats. Clarissa tells Joe it's all over, but his mind leaps to the pursuit of Mrs Logan's 'other woman'. Whatever he says to Clarissa is wrong. She's never seen Jed outside and the writing in the letters looks like Joe's. She's frightened, we can't believe Joe's being deserted now - but then again, is he imagining it all? It's separate beds time for Clarissa and Joe.
Joe meets Duty Inspector Linley to complain about the police's treatment of his harassment. Linley dismisses his claims. And so we move up a gear as, on Clarissa's birthday at a London restaurant the rather important politician sitting at the next table, Colin Tapp, is shot by hitmen. Joe is sure he was the intended target. The police don't. So, Joe goes home, looks through his address book and finds his only quasi-criminal friend - Johnny B Well, drugs supplier. Johnny takes Joe out to the country to meet some rather comical ex-hippies and buy a gun, as they leave Jed rings - he's got Clarissa captive in the flat. So now she probably believes Joe, she sounds scared anyway.
Joe almost poos his pants and practices with the gun. Joe gets back quick - Jed is sitting next to Clarissa, but despite the threat of a weapon he actually wants forgiveness from Joe - before ending his own life. "How can I forgive you when you're mad?" says Joe while pleasantly shooting Jed's elbow apart. Clarissa is horrified, things are definitely over now, as we discover from Clarissa's letter to Joe. Joe was right, but did he draw Jed in? Clarissa leaves the flat, but for how long?
There's still unfinished business. So Joe arranges a meeting for Jean Logan, the Euler Professor of Logic and 'that' woman. Clarissa comes too and there are difficulties between them. However, it's proved that the Professor, his nubile young lover and their picnic were given a lift by John Logan who was therefore not having an affair. Jean Logan forgives them, "but who's going to forgive me?". We end as the children ask Joe to tell the story about the river and how it's made up of tiny atoms "bound together by a mysterious force". We never get told what this force is.
There are two, in the first, a cod academic piece written by Wenn and Camia (an anagram of Ian McEwan) there is a scientific narration of the de Clerambault case we've just read. The characters 'R', 'P' and 'M' refer to the main characters' surnames as given in the novel. It is interesting to note the new information we get here: Clarissa and Joe are reconciled and adopt a child at a time beyond the end of the novel, whilst Jed is incarcerated in a secure institution. In the second appendix we get yet another letter from Jed, infatuation still going strong. What does this tell us about the nature of faith, and of love, an experience which "may merge into psychopathology"? Why does Jed effectively get the last word?