Queen of the Vampires

The Rape of the Vampire[edit]
Four sisters living in an old chÃ¢teau are convinced that they are vampires. One believes she was raped by the villagers years before, and is blind. Another is afraid of sunlight. They all react violently to crucifixes. The sisters are being manipulated by a sinister old man who alternates between admonishing them to kill newcomers that threaten their exposure, and groping their breasts. The four seem to worship a bestial idol in the forest who speaks to them with a disembodied voice.
The newcomers are three Parisians, Thomas (Bernard Letrou), Brigitte (Solange Pradle) and Marc (Marquis Polho), who have come to the countryside to cure the sisters of their so-called illness. They do not believe that the sisters are vampires, and don't believe in vampires at all. Thomas is a psychoanalyist, determined to cure them from their madness. He believes it has been induced by the superstitious villagers, who have driven the confused women insane with their religious symbols and persecution. He tries to convince them that crucifixes and sunlight won't harm them, and that the blind sister can actually see. He takes all of this as proof that their vampirism is all in their minds. When one of the sisters fall for Thomas' charms, the old man orders another sister to kill him, Brigitte and Marc. When this fails, he unleashes the peasants, who brutally murder all the women they can find, which also includes Brigitte.
Thomas asks one of the sisters to bite him to prove her wrong, and discovers she is, in fact, a vampire, and that he was misled by his own preconceptions. The two flee to the beach and are gunned down by Marc, who is distraught by Brigitte's death at the hands of the peasants.
Queen of the Vampires/The Vampire Woman[edit]
The vampire queen (Jacqueline Sieger) is introduced. She briefly arrives by boat to the beach where the dead couple lies. She commands her hooded cohort to grab the old man and pin him down to the slab of rock, then proceeds to sacrifice him, and licks the knife covered in his blood. The vampire queen tells her leading female minion to dismember the bodies of Thomas and the vampire sister so that they don't come back to life, but she fails. It is later revealed that she is in rebellion against the vampire queen. The blood from the old man revives Thomas and the vampire sister.
The human doctor who runs the demented clinic is under the supervision of the vampire queen and he has been secretly searching for a cure for vampirism.
The vampires abduct Brigitte's body from the cenotaph, and Thomas later discovers that Brigitte is alive. She tells him that he imagined the entire trip, but he doesn't believe her. He follows her to the hospital where she is listening to an instruction tape. He stops the tape and kills her.
The doctor's plot is later uncovered. While the vampire queen stages a ceremony to marry the doctor to his assistant, her minions strip the assistant and whip her on the beach. The malcontents have not bowed to her rule and the revolution explodes, which ends with the vampires being killed and the vampire queen poisoned. Thomas and the vampire wall themselves in the cellar to await death. They do not wish to feed on the living, but are too afraid that if they stay free, their thirst will drive them to murder, so they sacrifice themselves instead, ending their freedom in each other's arms.[3]

Question: What has the human doctor secretly been searching for?
Answer: A cure for vampirism