When the wealthy Emily Inglethorp is found dead from strychnine poisoning at her country estate, a retired Belgian detective must navigate a web of family secrets to identify the killer. Captain Arthur Hastings, recovering from war injuries, finds his quiet retreat at Styles Court shattered by the sudden death of his hostess. He enlists the aid of his friend, Hercule Poirot, who applies his meticulous, logical methodology to a household filled with suspects who all possess motives and hidden agendas. The narrative unfolds through Hastings' first-person perspective, documenting the intricate clues and psychological games that define the investigation.

As the debut novel of one of the most prolific mystery writers in history, this work is widely recognized for establishing the foundational tropes of the modern detective genre. Readers and critics frequently highlight the introduction of Hercule Poirot as a pivotal moment in literary history, noting his distinct personality and methodical approach to crime. The narrative is often praised for its clever construction and the way it challenges the reader to solve the puzzle alongside the protagonist. It remains a staple of the genre, serving as a primary reference point for the evolution of the whodunit format.