On the morning of 18 July, the household at Styles Court wakes to the discovery that Emily Inglethorp, the elderly owner, has died. She had been poisoned with strychnine. Arthur Hastings, a soldier from the Western Front staying at this country manor as a guest on his sick leave, ventures out to the nearby village of Styles St Mary to enlist help from his friend Hercule Poirot. Emily was a wealthy woman. Her household includes her husband, Alfred Inglethorp, a younger man she recently married; her stepsons (from her first husband's previous marriage) John and Lawrence Cavendish; John's wife Mary Cavendish; Cynthia Murdoch, the daughter of a deceased friend of the family; and Evelyn Howard, Emily's companion.
Poirot learns that, on Emily's death, John is to inherit the manor property, in accordance with his father's will. However, her money will be distributed according to her own will, which she changes at least once a year; her most recent will favours Alfred, who will now inherit her fortune. On the day of the murder, Emily had been arguing with someone, suspected to be either Alfred or John. She had been quite distressed after this and apparently made a new will. No one can find any evidence of this new will. Alfred left the manor early that evening and stayed overnight in the village. When her body was found, the case had been forced open. Nobody can explain how or when the poison was administered to her, just Poirot can.
