Plot summary
Superintendent Spence visits Poirot to ask him to find evidence that would forestall the execution of James Bentley, recently convicted of killing his elderly landlady, Mrs McGinty, for a meager £30. All evidence points to his guilt, but something about Bentley's dreary acceptance of his fate just doesn't sit right with the experienced Spence. Poirot agrees to go to the village of Broadhinny and investigate the murder. Taking a room in the Summerhayes' guest house, Poirot finds that Mrs McGinty often worked as a charwoman at various village houses. He also discovers that most of the townsfolk believe that Bentley is guilty.
During the course of his investigations, Poirot discovers that, three days before the murder, Mrs McGinty took a clipping from a notorious Sunday newspaper. The clipping showed photos of four females who had disappeared after having been involved in decades-old criminal cases. Mrs McGinty wrote to the paper, claiming to have found a similar photo, proving one of her neighbors was really one of the women in the article. However, her terrible spelling had caused the paper to dismiss her as a simple fame-seeker.
Poirot and Spence, going by the ages of the people in the town, conclude that someone is either Lily Gamboll, who committed murder with a meat cleaver at 12 years of age, or Eva Kane, a governess who'd had an affair with her employer, Arthur Craig. Craig was later convicted and executed for killing his wife, though the police believed it was actually Eva's doing. After being acquitted as an accessory, a pregnant Eva had changed her surname to "Hope" and left the country. Some sources claim she had a child named Evelyn, and several women in the town are the right age to be Evelyn, as well.
Shortly afterwards, Poirot discovers an old sugar cutter with traces of blood on it in the Summerhayes' house; the house is untidy and never locked, and the hammer was accessible to anyone. In an attempt to flush out the murderer, Poirot claims to know more than he does; later, someone tries to push him under an oncoming train, proving that the guilty party is still at large. Having acquired originals of the photos used in the article, Poirot shows them to the villagers at a gathering at elderly, wealthy Mrs Laura Upward's house. Mrs Upward claims to have seen the photo of Lily Gamboll, but refuses to say where.
Later, Poirot is contacted by Maude Williams, who had worked at an estate agent's with Bentley in another town before Bentley was laid off. She refuses to believe he is capable of murder, and offers to help Poirot. He accepts, and gets her to pose as a maid in the house of Mrs Wetherby, one of the houses Mrs McGinty cleaned. Poirot has already noticed that Mrs Wetherby's daughter by her first marriage, Deirdre Henderson, also believes in Bentley's innocence.
During the maid's night off, Mrs Upward's spoiled son, playwright Robin Upward, goes to the theatre with famed mystery writer Ariadne Oliver, whose novel he is planning to dramatize. When they return home, they find Mrs Upward strangled to death. She has evidently had coffee with her murderer; there is lipstick on a cup and perfume in the air, which point to a woman having committed the crime. Mrs Upward had invited three people to her house that night: Eve Carpenter, Deirdre Henderson, and Shelagh Rendell. Only Henderson came, but she found the house dark, and left. Any of the three women could be someone from the photographs. Additionally, the postmistress's assistant, Edna, saw someone with blonde hair enter the house; Carpenter and Rendell are blonde, but Henderson is brunette.
A book is discovered in the Upward house with Evelyn Hope's signature written on the flyleaf, suggesting that Mrs Upward was actually Eva Kane, further confusing the situation. Poirot then finds a photo in a drawer at the Summerhayes' house, and realizes it must be the photo Mrs McGinty saw. It is of Eva Kane, with the inscription "my mother" on the back. Recognizing the handwriting, Poirot gathers the suspects together and accuses Robin Upward of the murders, startling him into a confession.
Robin Upward is Eva Kane's son, Evelyn Hope; the real Robin Upward died young while his family had been living abroad. Too proud to be pitied as a childless widow, Mrs Upward began taking in promising young men as replacement "sons", dropping them if they proved unsatisfactory. Evelyn Hope had been the most successful of these protégés - he legally changed his name to Robin Upward and moved to Broadhinny with Mrs Upward, where no one knew him. Mrs McGinty, however, found the photo of Eva Kane in the house while cleaning it, and blackmailed Evelyn with it, believing it was a photo of Mrs Upward as a young woman.
Evelyn, knowing that being revealed as a murderer's son would put an end to his use of Mrs Upward's money, stole the sugar cutter and killed Mrs McGinty. He then framed Bentley by stealing £30, correctly assuming Bentley would panic and incriminate himself. When Mrs Upward saw the four photos at the party, she had recognized Eva Kane, but pointed to Lily Gamboll to throw Poirot off the scent, wishing to confront Evelyn in her own time.
Evelyn suspected the truth; pretending to forget something on the night of his play, he left Mrs Oliver waiting in the car, went back inside and strangled Mrs Upward. He planted the evidence of a female visitor, then, pretending to be his mother, he called Miss Henderson, Mrs Carpenter and Mrs Rendell in turn, hoping one of the women would come over and inadvertently incriminate herself. When this failed, he planted the photo in a drawer at Mrs Summerhayes' house, hoping to incriminate her. Unfortunately, Poirot had recently tidied up the same drawer, which proved the photo had not been there before Evelyn came to the house.
Further revelations are also made: Eve Carpenter wanted to conceal her past from her aristocratic husband, which was why she would not co-operate in the investigation. Spence discovers that Shelagh Rendell has been receiving poison pen letters claiming that her husband murdered his first wife; Poirot suspects that it was Dr Rendell who tried to kill him at the train station. Maude Williams turns out to be the Craigs' legitimate child; like the police, she believed Eva was the one who really killed her mother, and that her father chivalrously took the blame. Maude was also aware of Evelyn Hope's true identity, and went to Mrs Upward's house to confront her, believing her to be an aged Eva Kane. When Maude found Mrs Upward's body, she feared she might be accused of the murder and fled. Poirot agrees to keep this a secret, and wishes her good luck in her life. Deirdre Henderson has inheritance money of her own, which is why her malingering mother and her stepfather have been jealously mistreating her. She and Bentley also have romantic feelings for each other. Bentley is freed, and Spence is convinced they have closed the case at last, much to Poirot's relief.
