Hercule Poirot must untangle a seemingly impossible murder case when a socialite is accused of killing her estranged husband despite having a rock-solid alibi. The detective finds himself caught in a web of deception after Jane, Lady Edgware, publicly declares her intent to dispose of her spouse, only for the man to be found dead shortly thereafter. Poirot faces the logical paradox of a suspect who was witnessed dining with friends at the exact moment the crime occurred in a locked library. The narrative follows Poirot's methodical investigation as he navigates the social circles of the British aristocracy to uncover the truth behind the conflicting testimonies and hidden motives.

This novel remains a staple of the golden age of detective fiction, celebrated for its clever manipulation of the reader's perception. The central puzzle of the impossible alibi is widely regarded as one of Christie's most effective uses of misdirection. Readers often highlight the interplay between Poirot's sharp intellect and the seemingly transparent nature of the primary suspect. The work continues to be analyzed for its structural precision and its ability to maintain suspense despite the absence of overt physical action. It stands as a definitive example of the classic whodunit format that defines the genre's enduring appeal.