Hercule Poirot faces a serial killer who taunts him by committing murders in alphabetical order according to the locations and victims' names. Poirot must navigate a series of calculated crimes where the killer, known only as 'A.B.C.', leaves a railway guide at each scene to signal the next target. The detective is forced to rely on his psychological insight and logical deduction to identify the perpetrator before the next letter of the alphabet is reached. The narrative framework utilizes a mix of third-person perspective and epistolary elements, including letters sent by the killer to Poirot, which heighten the sense of urgency and direct confrontation.

This novel is widely regarded as one of the most innovative entries in the Christie canon due to its departure from the standard country-house mystery format. Critics often highlight the effectiveness of the serial killer premise in creating a sense of mounting dread that persists throughout the investigation. Readers frequently note the cleverness of the alphabetical gimmick, which serves as both a structural device and a psychological trap for the protagonist. The work remains a staple of the genre, frequently cited for its influence on the development of the modern procedural thriller. The balance between Poirot's methodical approach and the chaotic nature of the crimes provides a compelling contrast that sustains interest until the final reveal.