Synopsis
People are dying in the German town of Kleinschloss. They are found dead in bed and drained of blood. Burgermeister Gustave Schoen [Lionel Belmore] thinks that vampires are at large, but Detective Karl Brettschneider [Melvyn Douglas] thinks otherwise. When several people report being attacked by a giant bat, suspicion falls on Herman Gleib [Dwight Frye], the village idiot, who is known for befriending bats. When another person dies, Dr Otto von Niemann [Lionel Atwill] is called in to examine her body. He concurs with the vampirismtheory. When yet another person is found dead, the word goes out that Herman must be captured. In the meantime, von Niemann's maid Georgiana [Stella Adams] finds the crucifix of one of the victims in the bedroom of von Niemann's assistant, Emil Borst [Robert Frazer], and remembers that there were muddy footprints in Emil's bedroom the morning after a victim was murdered. At the same time, however, Herman is tracked to a cave but, when the townspeople attempt to take him, he panics and falls off a ledge. He is killed, and the townspeople finish the job by driving a stake through his heart. Not knowing about Herman's death, von Niemann has hypnotized Emil to attack Georgiana in the same manner as the other victims. Emil brings her body to von Niemann's lab where she is hooked up to a machine which sucks the blood from two woundsmade in her neck by a metal wraparound collar. A bit later, Karl and his girlfriend Ruth Bertin [Fay Wray] (who is also von Niemann's lab assistant) find Georgiana dead in her bedroom. Karl remembers that Herman was seen in the garden earlier that day, and the circumstantial case against him seems to tighten. However, when the Burgermeister reports Herman's death, Karl realizes that the timing is wrong and that Herman was innocent. He swears to search for clues, but Dr von Niemann advises him to first get a good night's sleep and gives him some sleeping pills to help. Later that night, Emil climbs over the roof to Karl's bedroom. Meanwhile, Ruth overhears von Niemann sending a mental suggestion to Emil, and she suspects the truth. Von Niemann confirms her suspicion, explaining that he has created a life form (looks like a sponge in a jar) that demands blood for its continued growth. Von Niemann takes Ruth to the laboratory where they find Karl waiting for him. "I didn't take your sleeping pills, Doctor," explains Karl. When von Niemann attempts to place the blame on Emil, Emil shoots him and then turns the gun on himself.