Tommy and Tuppence meet a mysterious woman at lunch one day. She sends them a note and asks them to visit her as they may be able to help. On their way to the house where she is staying, they run into a policeman who seems to appear out of the mist. As they chat, an angry man runs up to the house, bangs on the door and storms in. When Tommy and Tuppence arrive in the house, they are greeted by the mistress of the house, who happen to be the woman’s sister. She says that her sister is seeking a divorce from her husband. Together, they find the woman dead. They all all assume that the angry man who barged into the house was her husband and that he killed her when in fact it was the policeman who was her husband and the murderer.