Arthur Hastings, on sick leave during WWI, discovers Emily Inglethorp, the wealthy owner of Styles Court, has died from strychnine poisoning. Hercule Poirot, a friend of Emily's, helps investigate the case. Emily's husband, Alfred, inherits the manor property, but her fortune is distributed according to her own will. On the day of the murder, Emily had a dispute with someone suspected to be either Alfred or John. Alfred left the manor early, and Emily's body was found. Inspector Japp suspects Alfred, but Poirot argues that Alfred's behavior is suspicious and he cannot have purchased the poison. John is arrested, and Poirot's investigations reveal that Alfred committed the murder with Evelyn Howard's help. They added bromide to Emily's medicine, making the final dose lethal. They framed John as part of their plan, and evidence against him was fabricated. Poirot prevents Japp from arresting Alfred because he saw Alfred wanted to be arrested.
