At Dr. Oliver Stuart's office, Rosa East arrives beautiful and terrified. She tells her she is twenty-five years old and is married to a man who is forty years older than her; this man is rich and sick and the two hate each other. Rosa East adds that her husband always tells her that a patient cared for by her wife runs the risk of dying from poisoning. She tries to think that he is joking, but gradually, she falls into an obsession. Shortly after, Mr. East dies on his property in Hinton St. Luke of a heart attack. Arthur Crook, the memorable detective from "Don't open that door!" and "People die slowly", investigates the enigma.