Russian beauty Anita Mellikovna, traveling by train with a forged passport and carrying jewels, finds the police on her tail. Seeing Deene Maxwell, whom she met one summer in Scotland, on a train across the tracks, Anita climbs out of her train and enters his compartment. Deene, a British official traveling to Moscow, suggests they pose as husband and wife, since he has diplomatic immunity, and offers to marry her at the British Embassy. After the wedding, Anita reveals that she is already married to an eccentric, violent composer, Louis Capristi, whom she left on their wedding night after he threatened her. Meanwhile, Capristi, under the name Charles Pringle, is imprisoned in an English asylum for the criminally insane since he strangled a woman to death. Anita and Deene are happily in love in England when they are confronted by Capristi, who escaped after he heard about their marriage. Capristi threatens to have them arrested for bigamy unless they allow him to stay a few days until his boat for South America sails. Deene's friend, Scotland Yard Inspector Slante, becomes suspicious of Capristi and posts guards to watch him. One evening in a restaurant in Soho, the French girl Mariette recognizes Capristi as Pringle, and he murders her. Disguising his voice, Capristi calls Deene and lures him out of the house by telling him to meet Slante at Mariette's apartment.