Rachel Argyle, mother of five adopted children, is murdered and immediately, the rest of the family just assumes that Jacko, one of her sons, must be the murderer because he threatened to kill her earlier that same evening. Two years later, a man shows up at the Argyle's mansion and confirms what Jacko has told the police all along: he was hitchhiking at the time of the murder and in the company of that very man. Now, the Argyles have to deal not only with the loss of an innocent family member but also with the knowledge that someone else amongst them must have murdered Rachel Argyle. Fortunately, Miss Marple is on hand to find the guilty party, but it's not before the deaths of other innocent people that she can reveal the truth.