Talented soprano Marcellina (June Vincent) is murdered by her jealous boyfriend, Doctor Hohner (Karloff), who successfully hides the body and covers up his crime. Ten years later, another talented soprano named Angela (Foster) arrives at the Royal Theater. Hohner becomes obsessed with the idea that Angela's singing voice sounds exactly like Marcellina's. Using his position as Chief Physician for the theater, he secretly begins to hypnotize Angela into being unable to sing. Angela's boyfriend Franz (Bey) and housekeeper Louise (Gale Sondergaard) do some investigating and realize that the Doctor's sad tale of being abandoned by Marcellina doesn't add up- and that he has sinister plans in store for Angela.