This text details the investigative process of Hercule Poirot following the mysterious poisoning of Mrs. Inglethorp at her estate, Styles Court. The narrative follows Hastings, a guest at the house, as he observes a complex web of family tensions, including a bitter inheritance dispute and the suspicious presence of the victim’s new husband, Alfred Inglethorp. Poirot meticulously examines physical evidence, such as shattered coffee cups and a disguise, while navigating the misleading behavior of the Cavendish brothers and their wives. Ultimately, the detective reveals that the murder was a collaborative scheme orchestrated by Alfred Inglethorp and Evelyn Howard to frame the family. Through his signature logic, Poirot demonstrates how a chemical reaction in the victim's medicine was used to deliver a fatal dose of strychnine. The resolution not only identifies the killers but also repairs the fractured marriage of John and Mary Cavendish.