Architect Guy Haines wants to divorce his unfaithful wife, Miriam, in order to marry the woman he loves, Anne Faulkner. While on a train to see his wife, he meets Charles Anthony Bruno, who develops his idea to exchange murders: Bruno will kill Miriam if Guy kills Bruno's abusive father; neither of them will have a motive, and the police will have no reason to suspect either of them. Guy does not take Bruno seriously, but Bruno kills Guy's wife while Guy is away in Mexico.