A series of murders in Michigan lead an American secret agent to Amsterdam, where he uncovers a plot to imperil the world with a potent new drug.

A beautiful virgin inherits a castle, but when she arrives at it, she finds that the inhabitants include a strange nobleman and a bevy of beautiful women she suspects may be vampires.

Count Karnstein sends for a doctor to help his sick daughter Laura. Her nurse believes she is possessed by the spirit of a dead ancestor, Carmilla. A young woman becomes intrigued by the mysterious deaths surrounding Laura after a carriage accident outside the castle forces her to stay. They become close friends until Laura becomes convinced the spirit of Carmilla is forcing her to kill.