When I Kill You

The novel opens with a prologue: Nell is trapped in her darkened house after the electricity cuts out. A black-clad figure is already inside, blocking the stairs and forcing her into the kitchen. Cornered behind the island, she commands the figure to stop and demands to know who they are. The narrative then jumps back to trace the events leading to this moment.

The story alternates between two timelines. In the present, Nell Masters is a 36-year-old woman who manages Drop In, a charity in Brixton, London. She lives alone in a small mews house in Paddington inherited from her great-aunt. For weeks she has felt someone watching her, though she has never caught the person. Her real name is Elle Nugent, changed years ago, and she believes her former life will eventually catch up with her. Her boyfriend, Alex Stanton, is a 44-year-old French-American consultant who divides his time between Washington, DC, and London.

In the past, Elle is 22 and living near Waterloo with her boyfriend, Jaz. She witnesses a young woman's phone being snatched by a man on a moped. A dark-haired man with an American accent pulls up in a black car and offers to chase the thief; the young woman jumps in. Uneasy, Elle calls the police and provides descriptions. The next morning, 19-year-old Bryony Sanders, an American student at King's College London, is found dead in a burned-out car near Wimbledon Common. Elle is certain Bryony is the woman she saw.

Elle gives a detailed statement to Detective Constable (DC) Gail Moss and helps create a sketch of the driver. Months pass with no arrest, and Elle grows consumed by guilt. After spotting a man in a pub whose voice she recognizes as the driver's, she follows him to a house in St. John's Wood and learns through a ruse that his name is Brett Parker. DC Moss warns Elle not to pursue suspects on her own.

Interspersed throughout the novel are entries from "Notebook 4," written in second person and addressed to Nell by an unnamed stalker who has tracked her for months, cataloging her routines and movements. Each entry ends with a chilling variation threatening to kill her.

In the present, Nell learns that Alex's previous girlfriend, Ariane, was murdered in an apparent burglary at her Belgravia flat. When Nell searches online, she finds no media coverage, deepening her unease. At a dinner with Alex's sister Béatrice, Béatrice's husband Victor, and Béatrice's friend Inès, who works at the French Consulate, Inès accidentally mentions someone named Caitlin. Béatrice explains that Caitlin, another of Alex's former girlfriends, died in a skiing accident in Verbier nearly four years earlier after becoming separated from the group and skiing off the edge of a ravine. Nell is deeply unsettled that two of Alex's girlfriends have died.

Days later, Nell senses someone has been inside her house. Sadie, her assistant at Drop In, and Sadie's partner Simon, a police dog handler, investigate with their German shepherd, Kintyre, but find no signs of forced entry. Simon concludes someone skilled picked the lock and advises Nell to change her locks.

Alex arrives at Nell's workplace after learning she knows about Caitlin. He calls out, and Nell, unable to tell whether he said "Nell" or "Elle," spins around with her key raised as a weapon before recognizing him. He explains he kept Caitlin secret because admitting two dead girlfriends would have driven Nell away. He also reveals that Ariane secretly worked for the DGSE, the French foreign intelligence service, and that her murder was never officially recognized. Inès later tells Nell that Ariane believed she had a stalker before she died. Stunned by the parallel to her own experience, Nell confides that she too feels she is being followed. Inès deflects suspicion toward Marcus, a friend who has shown romantic interest in Nell and recently bought the house across from hers.

In the past, Elle's obsession escalates. She follows Brett Parker daily, confronts him posing as a journalist, and calls him directly. DC Moss delivers a formal warning: Parker has been questioned and cleared. Elle's relationship with Jaz deteriorates, but she cannot stop. On a bank holiday, she follows Parker's family to a restaurant where they are celebrating his son Damon's 18th birthday. She watches from across the street. Damon spots her. Brett Parker storms out and crosses the road toward her without looking at traffic. He is struck by a car and killed.

Elle is charged with involuntary manslaughter and receives a suspended sentence. The media vilifies her as a stalker who hounded an innocent man to death. Then Damon begins stalking her. At Southwark tube station, he grabs her and shoves her onto the tracks. A bystander jumps down to help. The train stops in time for Elle, but another man near the platform edge is struck and killed. Damon is sentenced to 20 years for attempted murder.

Elle inherits the mews house, legally changes her name, and becomes Nell Masters. For years she lives in solitary atonement, working for charities and accepting that Damon will one day come for her.

In the present, Nell contacts DC Moss, now Superintendent Moss, hoping to learn about Damon's release. The superintendent reveals Damon is still in prison. She also reveals that Bryony Sanders's case has been reopened: A terminally ill former lecturer at King's College has confessed to the murder. He stalked Bryony, offered her a ride after the phone snatching, and strangled her at his flat before burning the car at Wimbledon Common. The man often adopted an American accent, explaining the voice Elle heard. He bears some resemblance to Brett Parker but is not the same person. Nell is devastated to learn she was entirely wrong. The superintendent warns that when the story breaks, Elle Nugent's name will resurface publicly.

On Christmas Eve, Sadie visits Nell and reveals she already knows Nell's true identity. They spend a warm evening together. On Christmas morning, Nell wakes on the sofa and goes upstairs to find Sadie dead in the bed, stabbed. A notebook entry reveals the stalker entered during the night, found a figure snoring in the bed, and drove a knife through the mattress from underneath, believing the figure was Nell.

Nell tells Alex her entire history as Elle Nugent, and he accepts her fully. At Sadie's funeral, Nell senses the stalker among the mourners and announces she plans to spend a night alone at her house, intending to draw the killer out. She arranges for Simon to set up surveillance in Marcus's house across the street. Marcus readily lends his keys, suggesting he is not the stalker. Alex gives Nell survival instructions before reluctantly leaving.

That evening, the electricity cuts, returning to the prologue's scene. The intruder forces Nell into the pitch-dark kitchen, where the glass light well has been painted black. The figure corners her behind the island. Nell shouts names to buy time while secretly peeling a knife free from sticky tape she fixed to the island's underside in advance. A female voice confirms Nell is right about Caitlin and Ariane but also very wrong. Nell recognizes the voice: It is Inès. As Inès attacks, Nell drives the knife forward and kills her. Simon and Kintyre charge from Marcus's house, and Alex, who never truly left, is with them. Beneath Inès's balaclava, her hair is short and brown; her glamorous public appearance was entirely fabricated.

Four months later, Nell and Alex are in Washington, DC, staying with Alex's father. Alex receives four notebooks found in Inès's flat. Together they read her account. Inès first saw Alex during a skiing trip in 2021, fell instantly in love, and reinvented herself to infiltrate his social circle through Béatrice. She killed Caitlin by forcing her off a ravine during a later skiing trip and murdered Ariane after learning that Ariane and Alex planned to marry. Inès's supposed flatmate and boyfriend never existed, and her flat contained a room dedicated to Alex, its walls covered with hundreds of photographs. The novel closes with Alex wrapping his arms around Nell and asking how many children they should have.