After his twin brother Elwyn's funeral, Dr. Lloyd Clayton burns all of Elwyn's books and papers on sorcery and the supernatural. Later, Elwyn's helper, hunchback Zolarr, accuses Lloyd of murdering his brother, but Lloyd knows that Elwyn fell from a cliff while he was attacking Lloyd. On the same night that Lloyd's ward, Gayle, announces her engagement to Dr. David Bently, Zolarr exhumes Elwyn's casket and Elwyn emerges as a vampire. Lloyd is mystified by the death of Elwyn's first victim, who appears to have died from extreme anemia, and is shocked by the sudden appearance of Elwyn, who vows revenge against Lloyd for killing him, and announces that he intends to make Gayle his disciple. After Elwyn attacks Gayle in her sleep, she grows gradually weaker and weaker from what appears to be a debilitating illness. When Lloyd confides in David that he suspects Elwyn's supernatural forces are causing Gayle's illness, David reluctantly accompanies Lloyd to Elwyn's crypt, and there they discover that his coffin is missing. When Lloyd resists his suggestion that he marry Gayle immediately and take her away, David confides to the sheriff his suspicion that Lloyd is slowly murdering Gayle for her inheritance. A local woman, Kate, whose daughter died mysteriously the year before, goes to Gayle's bedside and insists that she wear a cross as a protective measure. She then informs Lloyd that Elwyn is a vampire, and that Lloyd must burn Elwyn in his coffin by daylight in order to stop him. Elwyn sends Zolarr to remove the cross from Gayle's neck, but David catches the hunchback in Gayle's room and chases him out of the house. David is then shocked when he sees Elwyn materialize and realizes that Lloyd was telling the truth. The sheriff, meanwhile, warns Lloyd to leave town, but he refuses. Later, Zolarr murders Kate after finding her near Elwyn's coffin, and then moves the coffin to Elwyn's house. When a local man sees Elwyn walking away from his latest victim, he assumes it is Lloyd, and forms a vigilante group. While Lloyd goes to confront Elwyn at his house, David tries to delay the mob. A candle is knocked over during a struggle between Lloyd and Zolarr, and the house catches on fire. The mob finally overcomes David and storms over to Elwyn's flaming house, where they see Elwyn and Lloyd locked in mortal combat. By the time Lloyd kills Elwyn, he is surrounded by flames, and both he and his brother die in the pyre.