Based on a true story and the 1935 German film Mazurka, a singer shoots the seducer, who ruined her marriage, before he can seduce her daughter.
After her mother (Dorothy Peterson) leaves on a train, Lisa (Jane Bryan) and her friend Hildegard (Mary McGuire) get two tickets to a concert from stranger Michael Michailow (Basil Rathbone). After the concert, pianist Michailow invites Lisa to dinner. Lisa finds that Michailow has replaced her teacher. Michailow lectures and then kisses Lisa, who says she hates it. Lisa is happy to get a gown from her mother. Lisa meets Michailow secretly at a nightclub. Vera (Kay Francis) sings "One Hour of Romance." Vera sees Michailow kiss Lisa and faints. Michailow leaves with Lisa and is shot by Vera.
Lisa testifies, and Vera confesses she killed him. Vera objects to her suitcase being opened and gets the courtroom cleared because of public decency. Vera tells of 1912 Warsaw when she sang Michailow's mazurka. Vera is quitting to marry Leonid Kirov (Ian Hunter). Michailow tells Vera he loves her, but she says he loves only himself. Leonid comes in and kisses Vera. In 1915 Vera cares for her baby girl. At a charity ball Michailow dances with Vera, and the party moves to Michailow's place. He plays piano, and Vera sings "I Belong to You." Xenia jealously stalks out. After drinking, Vera is dizzy and stays, waking and going home in the morning. Leonid asks her what is wrong, but she can't tell him. Vera goes out to meet Michailow and tells him to leave her alone; but her husband Leonid sees them and walks away. The lawyer tells Vera that Leonid gets custody of the girl, and Vera must leave.
Vera tells the judges that she worked in cabarets. She learns that Leonid died and meets his wife and daughter Lisa, who does not know her mother did not give birth to her. That night Vera sees Michailow kiss Lisa and shoots him. Vera asks the judges not to let Lisa know. People, including Lisa, return to the courtroom. The prosecutor (Robert Barrat) asks for five years for second-degree murder. The judge (Donald Crisp) sentences Vera to three years and offers a pardon, because her motive was to save a young girl. After people leave, Lisa wishes Vera well, and Vera's spirit hugs Lisa. Then Vera walks off to jail.
This poignant drama based on an actual case of 1930 imitates the expressionism of its German model and thus gives American audiences something different. Though it seems to be a morality tale against a man who seduces young women, the reaction of murder is much worse than what he did. Yet as the case shows, such over-reaction is all too human.