Years ago, Dr. Hohner brutally murdered Marcellina, a renowned opera star, because her career came between them. On the tenth anniversary of her mysterious disappearance, the opera house's physician discovers that Angela, a young singer, has been chosen to sing "The Magic Voice." Believing Angela's voice is a reincarnation of his deceased love, Hohner is determined to prevent her from singing the Marcellina role.
While examining her throat in his laboratory, the physician hypnotizes her into thinking she can never sing again. In an effort to free Angela from Hohner's control, her fiancé, Franz, appeals to the King who orders Angela to give a command performance. During Franz’s absence, Hohner attempts to take her life, but the physician's housekeeper intervenes and accuses him of Marcellina's murder. As Angela sings "The Magic Voice," Hohner tries to stop her through mental telepathy, but the power of Franz's love triumphs. Escaping into a subterranean room containing Marcellina's body, the doctor accidentally disturbs a lighted bowl, causing a fiery explosion that kills both him and Marcellina.