The novel is set in England during World War I at Styles Court, an Essex country manor (also the setting of Curtain, Poirot's last case). Upon her husband's death, the wealthy widow, Emily Cavendish, inherited a life estate in Styles as well as the outright inheritance of the larger part of the late Mr. Cavendish's income. Mrs. Cavendish became Mrs. Inglethorp upon her recent remarriage to a much younger man, Alfred Inglethorp. Emily's two stepsons, John and Lawrence Cavendish, as well as John's wife Mary and several other people, also live at Styles. John Cavendish is the vested remainderman of Styles; that is, the property will pass to him automatically upon his stepmother's decease, as per his late father's will. The income left to Mrs Inglethorp by her late husband would be distributed as per Mrs. Inglethorp's own will. Late one night, the residents of Styles wake to find Emily Inglethorp dying of what proves to be strychnine poisoning. Lieutenant Hastings, a houseguest, enlists the help of his friend Hercule Poirot, who is staying in the nearby village, Styles St. Mary.