Frederick Clegg, a working class man, wins the lottery and becomes reasonably wealthy overnight. With his new money, Clegg moves to London and begins stalking Miranda, an art student from his neighborhood with whom he is obsessed. Clegg buys an isolated old house in the English countryside and remodels its cellar, making it suitable for someone to live there. Then, after memorizing Miranda’s schedule, Clegg finds her walking alone and attacks her with chloroform. He takes Miranda to his new home and forces her to live in his cellar. Clegg claims he kidnapped Miranda because he wants her to see that he is a good person and for her to fall in love with him. Miranda warns Clegg that this will never happen, but he insists that she stay with him nonetheless. Clegg treats Miranda as his guest: he feeds her three meals a day, buys her whatever she wants, and talks to her whenever she will let him. However, no matter how much she begs, he will not let her go free.
Miranda does her best to get whatever she can out of Clegg. She convinces him to let her have baths upstairs and to walk accompanied outside in the evening. She also tries to escape from Clegg several times, but each time she fails. No matter what she does, Clegg never reacts violently, even though her escape attempts make him upset. Having tried everything else, Miranda decides to seduce Clegg, thinking he must want sex from her. However, Clegg finds Miranda’s advances repulsive, and he is unable to achieve an erection. When Miranda asks him about this issue, he lies and says a psychologist told him he was impotent. After this interaction, Clegg loses his attraction to Miranda and their relationship grows more hostile. Miranda asks Clegg if she can move to a room upstairs, so Clegg lies and says he will let her after he remodels it. However, as payment, he wants to take nude pictures of Miranda that he can use as blackmail in case she ever escapes. Miranda rejects Clegg’s offer and, once again, their relationship becomes hostile. Shortly afterwards, Miranda and Clegg get into a heated verbal altercation because Miranda tells Clegg he is not a real man. Feeling fed up with Miranda, Clegg knocks her out with chloroform, strips her naked, and then takes pictures of her. Around the same time, Miranda falls deathly ill and begs Clegg to take her to a doctor. At first, Clegg thinks Miranda is lying. However, soon he realizes her illness is real, so he tries to procure her some medicine.
At this point, the novel’s perspective flips, and its events are retold through Miranda’s point of view via a series of journal entries. Largely, Miranda’s story lines up with Clegg’s, though certain details are filled in, such as how Miranda went about her various escape attempts. Although Miranda’s journal entries do discuss Clegg, many of them see her reflecting on her past. In particular, Miranda writes a lot about her relationship with a much older male painter named G.P. Miranda becomes infatuated with G.P. shortly after she begins attending art school and regularly finds herself in his company. In particular, Miranda respects G.P.’s views on politics and art, which largely resemble her current opinions. However, she quickly learns that G.P. is a notorious philanderer, which makes his personal life a mess. Eventually, G.P. asks Miranda to sleep with him. Miranda rejects his suggestion because she thinks it is a bad idea, but she still feels like she is in love with him. Ultimately, G.P. stops speaking to Miranda after he suddenly proposes to her and she rejects him. Miranda has mixed feelings about G.P. but would do anything to be with him again instead of being trapped in Clegg’s basement. The last of Miranda’s journal entries detail her declining health. They cut off as she is on the brink of death.
After Miranda’s journal ends, the novel switches back to Clegg’s perspective. At this point, Miranda’s health is rapidly declining, so Clegg tries to indirectly seek medical help. However, because he is too cautious, all of his attempts fail. Before long, Miranda dies. Clegg considers writing a suicide note portraying his relationship with Miranda as a sort of Romeo and Juliet relationship and then killing himself. However, before committing to this decision, he meets a drugstore clerk named Marian, who reminds him of Miranda. After this interaction, Clegg decides to bury Miranda in his backyard and then begins stalking Marian instead.