Les démons (1973)

In England, at an unspecified time, an old witch is burned at the stake and lays a curse on her executioners: Judge Jeffries, the sadistic Lady de Winter, and her lover, Renfield. Before she dies, she tells them that her two daughters will avenge her. Yet she has no officially acknowledged descendants. But they discover that she does indeed have two daughters who are nuns, born of an illegitimate union with an unknown father. Their names are Kathleen and Margaret, and they live at the convent of Blackmoor. Lady de Winter goes there and discovers that Kathleen is no longer a virgin, unlike her younger sister. Kathleen says that she has impure thoughts and that an emissary of the Devil “visits” her every night. Frightened by the witch’s threat, de Winter has her arrested and puts her through the same test her mother underwent, the “Judgment of God.” Like her mother, Kathleen has marks on her tongue, does not bleed when needles are driven into her body, and water evaporates on contact with her skin. She is immediately identified as a servant of the Devil and, as such, sentenced to be burned alive. But Lord de Winter frees Kathleen, while her sister Margaret, who remained at the convent, is in turn possessed by a satanic force. Their demonic vengeance begins.