While on vacation in London, Canadian Richard Hannay (Robert Donat) becomes embroiled in an international spy ring related to the mysterious "39 steps." Then he meets agent Annabella Smith (Lucie Mannheim), who is soon killed in his apartment. He must elude the police, who are hunting him for murder, while he tries to stop Professor Jordan (Godfrey Tearle) from sending secrets out of the country. Hannay is assisted by Pamela (Madeleine Carroll), an unwilling accomplice who discovers the truth.