Count Dracula arrives at the seaside Visarian home of Dr. Franz Edelman, a renowned surgeon, in hopes of finding a cure for his vampirism. After viewing Dracula's coffin and discovering an unknown parasite in his blood, the initially skeptical Edelman agrees to take the vampire's case. As Edelman begins his treatment of Dracula, Lawrence Talbot arrives at the castle and insists on seeing the surgeon. Turned away, Larry later transforms into a werewolf before the astonished eyes of Edelman, police inspector Holtz and Miliza Morelle, one of the surgeon's nurses. The next morning, Edelman offers to treat Larry with an experimental mold, but the werewolf jumps off a seaside cliff when he is told that he must wait until enough mold can be cultivated. That night, Edelman is lowered to sea-level in a boson's chair, where he rescues Larry from a cave and convinces him to live. Also found inside the cave is the Frankenstein Monster, encased in mud. Edelman begins to revive the creature, but is convinced to stop by Nina, his hunchbacked nurse. Meanwhile, Dracula becomes infatuated with Miliza and decides to remain a vampire. During his next blood transfusion, Dracula hypnotizes Edelman and Nina, then infects the surgeon with his own blood. Edelman and Nina awaken just in time to save Miliza from the vampire's lecherous clutches, and Dracula is killed when he is exposed to the sun's rays by Edelman. Realizing that he has become a vampire, Edelman offers to treat Nina immediately with the cultivated mold, but the nurse unselfishly insists that the surgeon cure Larry first. While recuperating from his treatment, Larry learns that a blood-thirsty Edelman has killed Zeigfried, one of his servants, but says nothing out of sympathy and gratitude. Larry then agrees to kill the physician should Edelman be unable to cure himself of his vampirism. Later, Larry walks out into the moonlight to discover that the treatment has been a success, while the vampire Edelman sneaks back into his laboratory and revives the Frankenstein monster. Edelman then kills Nina, forcing Larry to shoot and kill him. The monster chases after Larry, knocking over various chemicals and setting a fire in the laboratory. The police and villagers arrive just as Larry and Miliza flee and the monster and the castle are engulfed in flames.