Steve Adams leaves a man dead and bloody in a bathroom. Later, in a park, he sits next to a young woman lying dead on a picnic table. There, he remembers being a child in his father’s church, listening to a sermon, and receiving a blood transfusion from his father every month due to an illness. Steve also recalls drinking blood from the neck of his pet dog. Awakening form his reverie, Steve gets into his sports car and leaves the woman’s body on the picnic table. Later, two plainclothes police officers investigate the murder scene. One of them, assistant detective Butterfield, is visiting from Scotland Yard in England. When the American detective tells Butterfield that the woman is the twenty-sixth victim with puncture marks in her neck, the Englishman guesses the killer is a vampire. Meanwhile, a motorcyclist with a young woman riding behind him gets off his bike and accosts Steve with a knife. When he pushes Steve into an empty parked car, Steve turns into “Deafula,” a caped vampire. Deafula hypnotizes the biker and gives him instructions to tie his girl friend to the back of the motorcycle and drive off a cliff. Later, when the two policemen visit the crash scene, Butterfield suspects the vampire is involved. However, the American detective says they must leave, because they have a dinner appointment with his boyhood friend, Steve Adams. At that moment, Deafula creeps into the home of a woman and kills her. Later, as the two detectives wait for Steve at a restaurant, Butterfield recounts meeting Dracula and driving a stake through his heart. At that moment, Steve arrives. The American detective introduces him to Butterfield, shares a few childhood memories, and asks Steve if he has any ideas about the serial murders. Steve suggests people should stay home after sundown, but the detective reminds him that many of the victims were killed in their homes. Though Steve orders a meal, he eats peanuts without shelling them—“an old habit,” he says. After Steve leaves, Butterfield remarks on Steve’s strange habit. Later, Steve transforms into Deafula and chases an African American man through an alley before killing him. Two homeless men see the murder, but Steve hypnotizes them into stabbing his victim’s body with knives. As soon as the two detectives arrive, Butterfield sees teeth marks on the neck along with stab wounds. A television newscaster announces that police have found the twenty-ninth victim of the city’s serial killer. Meanwhile, Deafula appears in a woman’s bedroom, hypnotizes her, and drinks her blood. Later, Steve’s father tells him he can no longer give his son monthly transfusions due to heart problems. Now that Steve is almost thirty years old and graduated from a seminary, it is time for him to learn the truth. He shows Steve a letter from Amy, his late mother’s old friend. The father recounts going to Dr. Moon to find out why his wife, Maria, died during Steve’s birth. Moon took them to see Dr. Reichle, who examined baby Steve and said he had a rare blood disease without a cure, other than being kept alive with monthly blood transfusions. Now, in the present, Steve and his father ride in Steve’s sports car, and Mr. Adams asks if his son has considered marriage and children. Suddenly, Steve is sickened by his desire for fresh blood. He parks in a remote, wooded spot and runs from the car. Mr. Adams tries to give chase, but has a heart attack and falls down. Nearby, Steve kills a young couple by a lake. Now sated, he returns to his father and finds him on the ground. Mr. Adams gives Steve the old letter from Amy, tells his son where to find her, then dies. When the two detectives arrive later and interview Steve, Butterfield is curious about the two new vampire victims discovered only 200 yards away. He wonders why Steve brought his father to this remote place, but the other detective gets angry at Butterfield for casting suspicion on Steve. Butterfield leaves them and follows footprints between Mr. Adams and the two young victims. He also finds vomit containing peanuts and peanut shells. Elsewhere, Steve goes to Amy’s mansion and is greeted by a hunchback servant, Zork, whose hands are tin cans. When Steve informs Amy that his father is dead, she recounts his mother giving birth to him. She shows Steve a glass box with a ring inside and says it belongs to him. Amy says she knows when Steve kills by looking in the box, because the ring disappears whenever he transforms into Deafula. The ring reappears when he becomes Steve again. Amy says that when Maria was pregnant, they stayed together at a cabin while Steve’s father was away. One night, Maria began to convulse, and Amy ran for a doctor. When she returned, Maria was dead and her baby, Steve, was lying beside her on the floor. Amy took the ring off Maria’s finger, but saw evil in it, and when Steve’s father arrived, she kept it away from him. Later, Amy studied witchcraft. Back to the present, Amy tells Steve to look over his shoulder at Zork. When he does, Zork hypnotizes him by swaying a locket from a chain in his teeth. Steve has a vision of his mother in the woods with Dracula, who sucks her blood. After Steve awakens, Amy informs him that Dracula is his second father, and directs him to Dracula’s grave. At another mansion, Steve descends into a cellar cave and finds a coffin. Opening it, he tries to drive a wooden stake into Dracula’s heart, but a force pushes him back. Dracula rises from the coffin, and Steve asks the whereabouts of his mother, Maria Adams. Dracula points to an old crone in a black cowl, but when Steve refuses to believe him, the vampire transforms her into a young woman. Dracula yells at Maria for losing his “eternity ring,” and Steve takes advantage of the distraction by pushing him back into the coffin, driving a stake into his heart, and locking the lid. His mother turns to ashes. When Steve returns to his father’s home, he decides to take over his ministry. As he delivers a sermon to his father’s congregation and warns of the devil coming into the church, a little girl cuts her finger and sucks the blood. Afterward, as people leave the church, Butterfield and the detective meet Steve at the front door. Butterfield wants to arrest Steve as a vampire, and shows the detective a sample of the peanut-shell-filled vomit he found between the body of Steve’s father and the bodies of the two young lovers. Butterfield also admits that he asked his granddaughter to sit in the church where Steve could see her, prick her finger, and suck it. When Steve cringed, Butterfield knew he was guilty. Steve asks the detectives to leave him alone in the church for a moment. Wearing the eternity ring on his finger, Steve touches it to a large cross and visualizes Amy’s death and Zork regaining his hands. Steve picks up a small crucifix but it burns his hand. Asking God to forgive and cleanse him, Steve dies calmly. When the officers enter the chapel, the detective places the crucifix in Steve’s hand.