Poirot and his friend, Colonel Race, investigate. They discover that numerous passengers had motives to kill Linnet: Louise Bourget, Linnet's maid, was bitter due to her mistress' refusal to grant her a promised dowry; Andrew Pennington, Linnet's American trustee, was anxious to prevent her from discovering that he embezzled from her; Mrs. van Schuyler, an elderly American socialite suffering from kleptomania, displayed a great interest in Linnet's pearl necklace; van Schuyler's nurse, Miss Bowers, blamed Linnet's father for financially ruining her own father; Salome Otterbourne, a romance novelist, was being sued for libel for a similarity between Linnet and one of her characters; Mrs. Otterbourne's daughter, Rosalie, was anxious to protect her mother from financial ruin; Jim Ferguson, an outspoken Communist, resented Linnet's wealth; and Dr. Ludwig Bessner, a Swiss psychiatrist, faced exposure by Linnet concerning his unorthodox methods affecting Linnet's past friends.