Dr. Hohner (Karloff), the theatre physician of Vienna's Royal Theatre, murders his mistress, the star singer, after his jealousy drives him insane. Ten years later, another young singer (Foster) awakens Hohner's old enthusiasm. Hohner is determined to keep her from singing for anyone other than him, even if it means permanently silencing her. In the film's conclusion, the singer's fiancée (Bey) rushes to her aid.