The story begins in the English village of Woodleigh Common where the widow Rowena Drake is organizing a Halloween party in her garden. The atmosphere is festive until tragedy strikes during the party. Joyce Reynolds, a teenage guest, is found dead in the apple-bobbing tub. Joyce had earlier claimed to have witnessed a murder as a child, but her words were dismissed at the time.
In attendance is Ariadne Oliver who calls Detective Hercule Poirot to investigate the murder. Poirot teams up with retired Superintendent Spence and begins to compile a list of past events in the village. The investigations reveal several interesting facts including the mysterious deaths of Mrs. Llewellyn-Smythe, Leslie Ferrier, Charlotte Benfield, and Janet White. Poirot also uncovers connections between the victims and potential motives for their murders.
As the inquiry progresses, Poirot advises a search of the nearby forest resulting in the discovery of Olga Seminoff's body. It bears similarities to Ferrier's murder. Concerned for the safety of potential targets, Poirot intervenes to protect Judith and her daughter, Miranda. An attempt on Miranda's life reveals the truth behind the complex web of deceit and murders.
Miranda reveals that she had actually witnessed the murder claimed by Joyce, which implicates Michael Garfield and Rowena Drake. Poirot reconstructs the events and exposes Rowena as the mastermind behind the murders. She orchestrated them to cover up her earlier deceit regarding her aunt's fortune. The motive behind the murders was Garfield's insatiable desire to create a perfect garden funded by Rowena's inheritance.
In the end, Poirot concludes that Garfield's thirst for perfection would have eventually led to Rowena's demise. He further reveals Garfield as Miranda's father and outlines the intricate connections that unraveled during the investigation.
