I'm Not the Only Murderer in My Retirement Home

Carol Quinn, a 75-year-old convicted serial killer, arrives at Sheldon Oaks, a luxury retirement home in Hampstead, London, after 35 years in prison. She carries only a small wheelie case. Giles Temple, the home's owner, and Elisa, the concierge who manages daily operations, greet her with visible unease. Carol knows they debated the ethics of accepting her because they accidentally forwarded her their internal email exchange on the subject. They accepted her largely because she offered to buy an apartment outright in cash.

Carol joins a Tuesday baking group, where she meets Geoffrey Standing, a 75-year-old retired detective chief inspector (DCI); Margaret, a former home secretary, the UK cabinet minister overseeing policing and domestic security; Catherine, an elegant former pathologist; and Desmond Crisp, a cheerful former police official. Carol tells everyone she was a secretary who never married, both true, and no one presses further. When Geoffrey recognizes her surname, her anonymity crumbles. He was part of the police team that caught her decades earlier, and Margaret had pushed for a life sentence during her time in office. Geoffrey calls a private meeting with Margaret and Catherine to share the news.

Flashbacks reveal Carol's history. In the late 1970s, fed up with men who harassed and groped her, she began killing. Her first victim was Karl Chilvers, a regular at her local pub, whose cocaine she replaced with strychnine she had stolen while temping at a laboratory. Carol's victims were people she deemed deserving of death.

Back in the present, residents flinch and avoid Carol. While sitting on her balcony, she sees a body fall past her and hears rapid footsteps on the roof above. The dead man is Desmond. Carol notices a circular imprint on his forehead that does not match injuries from a fall.

Police arrive, led by DCI Bob Beattie, a disheveled senior detective, and his junior partner, Detective Sergeant (DS) Laura Welsh, an ambitious Scottish woman. After leaving the scene, Bob pulls over on Hampstead Heath to vomit and reveals he knew the victim: Sir Desmond Crisp, former head of the Metropolitan Police, whom Bob calls "scum." At a residents' meeting that evening, Bob announces the death is suspicious. Geoffrey publicly identifies Carol as a convicted serial killer and urges the police to bring her in for questioning. The room turns hostile.

Geoffrey proposes that he, Margaret, and Catherine investigate the murder themselves, convinced Carol is the killer. They confront Carol in her apartment, each carrying a makeshift weapon. Carol deduces they have formed a "murder club," insists she is innocent, and suggests they would make a formidable team, but recognizes they are not ready to include her. The trio attends Desmond's autopsy, arranged by Catherine through a former colleague. The findings reveal Desmond was poisoned, strangled with fabric, struck on the head with an object leaving a 45-millimeter circular imprint, and pushed from the roof. His last meal is identified as shepherd's pie.

Carol conducts her own investigation. She inspects the locked roof door and questions Tyler, Elisa's teenage son and the building's gardener, who refuses to share information. She also questions Jim, an elderly resident and former crime boss who controlled North London. Carol and Jim share a history: They once met in Epping Forest, each burying a body, and Jim helped Carol dig. Jim admits he argued with Desmond over an unpaid debt but refuses to elaborate. Carol investigates Shep Newsom as well, the husband of Desmond's daughter Hannah. Shep signed the Sheldon Oaks guest book 15 minutes before Desmond died, and Hannah has since inherited millions.

Feeling isolated, Carol fantasizes about returning to murder. At karaoke night, Belinda, a resident who proclaimed love for Desmond but is now involved with Marco, the young Italian waiter, throws wine in Carol's face. Carol's old instincts flare: She smashes a bottle and holds it to Belinda's throat but hesitates. Bob arrests her for Desmond's murder. In her cell, Carol cries for the first time this century, realizing her murderous rage has truly left her. She outmaneuvers the detectives during interrogation, secretly photographs the murder file, and is released when Margaret arrives to act as her lawyer.

Geoffrey and Catherine search Desmond's cleared-out apartment and find cannabis cakes. They deliberately eat a piece, hoping for investigative clarity, and discover the restaurant's weekly meal plan confirms shepherd's pie was served the day Desmond died, suggesting the poisoning may have occurred through his food rather than a spoon Carol handed him during baking. They later search Carol's apartment, where Catherine discovers journals filled with violent fantasies, poison dosages, and the word "Kill" repeated endlessly. Catherine declares Carol a "monster."

Carol confronts Elisa, who admits she engineered the Belinda confrontation to get Carol removed from the home. Elisa reveals Sheldon Oaks is in severe financial trouble and drops a crucial detail: Polly, an elderly crime novelist, was once married to Desmond. Carol interrogates Polly, who reveals Desmond got a waitress pregnant on their honeymoon in Ferragudo, Portugal, and never acknowledged the child. DS Welsh independently traces a fluorescent yarn fiber found on Desmond's body to Polly's special-order wool and takes her in for questioning.

Then Giles is found dead, locked in the building's sauna. This second murder clears Polly, who was in police custody at the time. Carol, Catherine, Geoffrey, and Margaret examine the body and find a tattoo reading "Waynflete," a house at Eton College, the elite boarding school. This connects Giles to Shep, a fellow Eton alumnus. Using face ID on the corpse, they unlock Giles's phone and find his last call was to Shep. Elisa catches them carrying the body, and all four are arrested. Laura releases them, accepting Carol's argument that they are embedded inside Sheldon Oaks and are the best hope of solving the case. Carol confirms with Polly that her honeymoon was in Ferragudo, the same town Elisa identified as her hometown, confirming Carol's theory that Elisa is Desmond's unacknowledged daughter.

Carol and Margaret visit MI5, Britain's domestic intelligence service, where Margaret's retained top-secret clearance grants access to files on Desmond's corruption and Jim's true past as an undercover police officer who infiltrated a crime gang but crossed over into genuine criminality. Meanwhile, Catherine and Geoffrey discover on Giles's phone that he was growing cannabis on the Sheldon Oaks roof. On the roof, they find Jim tending the plants. Jim attacks Geoffrey, and a violent struggle brings Geoffrey to the edge. Carol and Margaret arrive just in time. Carol pulls Geoffrey free and pins Jim down, feeling the old temptation to kill but recognizing she now has something to lose. Before she can release him, Catherine drives a pair of secateurs, or pruning shears, into Jim's neck to protect Geoffrey. Jim dies.

At karaoke night, Carol delivers her resolution before the assembled residents, police, and suspects. She reveals that Elisa is Desmond's illegitimate daughter from the Ferragudo affair. Elisa poisoned Desmond's cottage pie, correcting the autopsy's misidentification of shepherd's pie, with deadly nightshade from the gardens. Tyler struck Desmond with a gardening mallet matching the circular imprint, strangled him with gloved hands, and pushed him off the roof. The fluorescent fiber came from Tyler's jumper, knitted by Polly. Carol then reveals Bob killed Giles. Bob had protected Giles's rooftop cannabis operation in exchange for his mother Agatha's free residency at Sheldon Oaks. When Giles tried to blackmail him, Bob locked him in the sauna.

In the epilogue, Carol is back in prison, having taken the blame for Catherine's killing of Jim to protect her friend. She shares a cell with Elisa. Margaret, Catherine, and Geoffrey visit. Catherine and Geoffrey are engaged, and Margaret is working on an appeal arguing self-defense. The four friends laugh together over a lemon meringue pie recipe, their bond intact despite the bars between them.