When teenagers, Guy Curran led a street gang around Notting Hill, and went out with Leonora Chisholm. He is 19, handsome and powerful, she is thirteen and seeking rebellion. It was to him that she lost her virginity, and with him that she first experienced drugs. Guy is from an estate, of Irish origin, whilst Leonora is of middle-class English stock; from the start Guy feels antipathy from Leonora's mother, Tessa.
Guy is a drug dealer in his youth, and once gave some LSD to a man named Col McIlvanney. McIlvanney believes himself to be St Francis of Assisi and after taking the drugs is killed by an allergic reaction to bee stings. His friend Poppy Vasari tracks Guy down and swears revenge on him for McIlvanney's death. After this incident Guy gives up dealing, moves on to other schemes and makes a good deal of money.
Leonora grows up, goes away to University and restricts Guy to seeing her only on Saturdays for a weekly lunch. He tries to retain his stake in her life by calling her every day and by informing anyone who will listen of his love for her. He still believes, despite all the evidence to the contrary, that she still loves him as much as he does her and that one day she will come back to him.
Whilst speaking with a mutual friend, Danilo, Guy discovers that Leonora is to be married to William Newton, a man Guy refers to as 'the ginger dwarf'. Guy begins to believe that Leonora's close-knit family, including her parents and their new spouses and her brother Robin, and her friends Rachel and Meave have turned her against him. He also thinks that they have done this by telling Leonora he was involved in the death of McIlvanney. These beliefs and Guy's rage build up to the extent that he gets in to a physical fight with Leonora's brother, Robin, at a party. After this incident Guy asks Danilo to arrange for Robin Chisholm to be killed by a hit-man.
Whilst with Leonora Guy learns that a failed attempt to run-over Robin Chisholm has been made. He feigns sympathy for Robin although his girlfriend Meave is suspicious that he has tried to have Robin killed. After discovering that it couldn't have been Robin who told Leonora of his involvement in Col McIlvanney's death Guy calls off the hit-man and tells Danilo to set him on Leonora's friend and flatmate Rachel Lingard instead.
Leonora and Guy go for a meal at the Ritz, which is unusual as Leonora usually will not let Guy spend much on their lunches together despite his wealth. She dresses in a way that is pleasing to him and is affectionate to him, so much so that he asks who told her about his role in the death of Col McIlvanney. Leonora, who says that learning of this had no effect on her feelings for Guy at that time, confides that it was her stepmother, Susannah who had received a letter from Poppy Vasari. At the end of the meal they walk hand-in-hand and kiss passionately by the river Thames.
Leonora invites Guy for supper at her fiancé William's flat. Whilst there Guy learns that William has a new job with the BBC in Manchester and, going in to a fury, challenges William to a duel with some old swords. William, a fencer a University, slashes Guy's arm. Leonora takes him to hospital, gives him great sympathy and kisses Guy before asking him to spend the whole day on Saturday with her. It will be their last Saturday together before Leonora is married.
Guy, believing she is coming back to him, is filled with happiness as Saturday approaches and dresses carefully before meeting her for lunch. She never arrives at their meeting, so Guy, armed with a .22 rifle, goes around her family's homes trying to find Leonora, whom he believes to have been imprisoned by her family when they discovered she planned to leave William and return to him, Guy.
He arrives at Leonora's mother and stepfather's home to be told Leonora and all her family have tricked him in to believing she was to be married a week later and that, in fact, she was married whilst he was sat waiting for her to arrive for lunch. The plan was thought up by Leonora's stepmother, Susannah, and Guy plans to kill her and her husband.
He returns home, and too drunk to drive spends a comforting night with his girlfriend, Celeste. In the morning his anger has lessened and he hopes to start a new future with Celeste. Then he is arrested by the Police: the hit-man has killed a relative of Leonora's who looked like Rachel.