Carla Lemarchant was a child of five when her mother was accused and convicted of poisoning her father, the famous painter Amyas Crale. After Caroline Crale dies in prison, Carla is sent to live with her uncle and aunt in Canada. Only on her twenty-first birthday does Carla learn of her family history when she reads a letter written by Caroline before her death, in which she denies murdering her husband. But if her mother didn't kill Amyas Crale, who did? Carla needs to know, because she is planning to get married and wishes to start her new life without this terrible shadow hanging over her. Desperate to find out the truth, she consults the best detective money can buy. With nothing to go on except five suspects who fit strangely into the pattern of a child's nursery rhyme, Hercule Poirot is faced with a formidable challenge to find the real killer...