Espionage agents Valya (Jean Kent) and Zurta (Albert Lieven) break into an embassy in Paris to steal a diary filled with crucial political secrets. The spies pass the diary on to accomplice Karl (Bonar Colleano) -- who then double crosses them, fleeing on the Orient Express to sell it abroad. The agents go after Karl to regain the diary, and a police inspector pursues the agents -- while on the train, an unfaithful couple, a writer and a bird-watcher become unwitting participants in the drama.