Lisa Koslov, a young and innocent music Warsaw student, is seeing her mother, Mrs. Koslov, off at the train station when an elegant man offers her two tickets to a concert. She attends the performance and discovers that the mysterious stranger is the great pianist, Michael Michailow. Lisa is frightened by his worldliness but is flattered by his attention and agrees to dine with him. At a sophisticated restaurant, they are seen together from the stage by the chanteuse, Vera Kowalska. Driven by some unspoken passion, she shoots and kills Michael. On trial, Vera refuses to reveal her motivation, but when Michael's suitcase is introduced as evidence, she begs the court to hear her story before they examine it. She explains that she was once married to Leonide Kirow and was devoted to him and their child. While he was away at war, she attended a ball where she encountered Michael, who had been her conductor when she was a well-known opera singer before her marriage. Although Vera refused his advances, he persisted, and intoxicated, she spent the night with him. Leonide returned home wounded, discovered the situation and divorced her, taking custody of their child. Leonide changed his name, remarried and died, after which his widow reared Vera's child. The night Michael was shot, Vera confesses, she recognized that he was planning to seduce her daughter. Vera begs the judge not to make her confession public and to protect Lisa's reputation. The court concludes that Vera's actions were justified, and her sentence is minimal.