A young girl's boast of witnessing a murder turns fatal when she is found dead at a Halloween party, prompting Hercule Poirot to investigate the dark secrets of a quiet village. Poirot arrives in Woodleigh Common to assist his friend Ariadne Oliver, who is distressed by the girl's sudden demise. He must navigate a web of local gossip, long-buried resentments, and deceptive appearances to identify a killer who strikes to protect a hidden past. The narrative follows a traditional third-person perspective, focusing on the meticulous gathering of clues and the psychological unraveling of suspects.

This novel is widely recognized as a late-career entry in the Hercule Poirot series, often noted for its darker tone compared to earlier works. Readers frequently highlight the inclusion of Ariadne Oliver as a standout element, providing a meta-fictional layer to the investigation. The mystery is often praised for its intricate plotting and the clever way it weaves local history into the central crime. While some critics suggest the pacing reflects the author's later style, the consensus remains that it delivers the classic puzzle-solving experience expected from the genre.