John George Haigh Martin Clunes grows up in a small Yorkshire village under the sway of strict Plymouth Brethren beliefs, where his parents insist their family sits apart from the rest as part of God's elect. As an adult, Haigh slides into petty crime, and his marriage to Beatrice 'Betty' Hamer Sally Carman results in a pregnancy that colors his ambitions and fears. While serving a sentence for fraud, he encounters the phrase corpus delicti and misreads it as proof that murder can’t be proven without a body. With that mistaken certainty, he dreams of a perfect murder and begins testing ideas by dissolving mice in sulphuric acid, a grim prelude to a pattern he will later expand on.
After his release, Haigh goes to London and tries his hand as an engineer, only to be fired after a relationship with his boss’s daughter, Gillian Rogers Keeley Hawes. He then reinvent s himself as an inventor and reconnects with Donald McSwan Neil McKinven, a successful property entrepreneur, and his elderly parents, William and Amy McSwan Donald Douglas and Claire Nielson. Haigh offers to help them during World War II, proposing that Donald run the business and care for his parents while Donald serves abroad in Scotland. Instead of support, Haigh bludgeons Donald to death in his workshop, dissolves the body in acid, and forges Donald’s signature to take control of Donald’s affairs. He sustains the sham that Donald is on the run for the duration of the conflict, but as VE Day arrives, Haigh deceives William and Amy about Donald’s return and then kills them to access their savings. With that wealth, he moves into the Onslow Court Hotel in Kensington, living off the illusion of fortune.
Haigh’s next targets are Archie and Rose Henderson, a doctor and his wife who become entangled in Haigh’s web of manipulation after Haigh befriends them. Archie is invited to Haigh’s workshop and murdered there, while Rose is later lured under the pretense that her husband is ill, only to meet the same fate. The couple’s friend Arnold Burton John Flanagan grows suspicious when Arnold notices discrepancies in the Hendersons’ affairs, and a shadow of doubt begins to fall on Haigh’s harmless pretenses. The couple’s wealth and business dealings are folded into Haigh’s scheme, a pattern that continues even as Haigh’s funds start running low.
Haigh then targets Olive Durand-Deacon Rowena Cooper, a resident of Onslow Court, and, when Olive disappears, her friend Constance Lane Matyelok Gibbs grows uneasy enough to persuade Haigh to accompany her to the police to report the missing neighbor. The pressure from the case grows as Detective Sergeant Heslin Terence Beesley and other investigators close in, and a Home Office pathologist is called to Haigh’s workshop, where gallstones and a pelvic bone are recovered as grisly corroboration of the murders. Haigh ultimately confesses to the police: he murdered Olive by dissolving her in acid and claims six additional killings, suggesting there may be other victims. Convicted of murder, Haigh awaits a death sentence, a moment tempered by the presence of Gillian Rogers, who Haigh asks to visit his parents after he is hanged.
In a final, quiet coda, Gillian Rogers honors that promise, bearing witness to the consequences of Haigh’s calculated depravity. The story presents a meticulous, chilling arc of deception, betrayal, and the lure of easy money, tracing Haigh’s gradual arc from a sheltered upbringing to a calculated killer who exploited trust, wealth, and opportunity across a wartime Britain.
