Set in the 17th century. A convent in a small town is being visited by high-ranking Catholic official trying to exorcise the nun supposedly possessed by demons. A local priest have been burnt for creating this condition by sexual temptation of the nuns, especially the Mother superior who bring on the collective hysteria of the group. There is another young priest who is to help with the exorcism. His first meeting with the convent head, Mother Joanne of the Angels, has her seemingly possessed by Satan - she yells blasphemies and incites the priest. She begs the priest to save her and to help her to be a saint. To help her, he kills two innocent people to be forever a prey of the devil and thus allow her freedom.