A young woman bursts into Hercule Poirot's breakfast to confess to a murder, only to vanish before he can determine if she is a killer, a victim, or suffering from a delusion. Poirot must navigate the shifting social landscape of 1960s London to uncover the truth behind the girl's claims, facing a web of family secrets and elusive witnesses. The narrative follows the detective's methodical process as he attempts to distinguish between genuine criminal intent and the psychological instability of the suspects. The story unfolds through a traditional third-person perspective, emphasizing the contrast between Poirot's classic sensibilities and the changing cultural norms of the era.

This novel is often noted for its departure from the traditional country house setting in favor of the vibrant, changing atmosphere of mid-sixties London. Readers frequently highlight the inclusion of Ariadne Oliver, whose presence provides a sharp, humorous counterpoint to Poirot's more rigid investigative methods. The narrative is often analyzed for its reflection of Christie's own observations on the shifting social mores of the younger generation during that decade. While some critics suggest the plot is less tightly constructed than her earlier works, the character dynamics remain a primary draw for those interested in the evolution of the series.