Sixteen years before the action opens, Caroline Crale was charged with killing her husband, Amyas Crale, and no one doubted her guilt. She was duly tried and convicted, and died in prison while serving life, so the case was looked on as closed. But then, in the present day, Caroline's daughter Lucy Crale (who has been living overseas) receives a letter her mother wrote her before her death, claiming to be innocent. Anxious to know the truth, Lucy hires Poirot to solve the murder of her father sixteen years before, and Poirot finds a number of possible suspects who are still alive. The late lamented Amyas was well-known for having affairs with his models. Does Elsa Greer, his lover at the time of his death, hold the key to unravelling the case?