The peace of a Nuns' Convent is destroyed first by a mystifying killing, and secondly by a series of inexplicable phenomena. The nuns, in their way of thinking, believe it to be the work of the Devil. The Mother Superior calls in a priest, immediately, to exorcise the Convent but this provokes another murder, and further terror. A second younger, more modem priest, Father Valerio - an expert in parapsychology - is next to intervene. He feels the nuns are hos-tile to him, and avoid him, and stimulated by this, is determined to go on until he finds the answer. More violence and murders - in-cluding that of the exorcist - endanger his life, and mercilessly shake his faith in God. Father Valerio, at this point, meets Elisa, the illegitimate daughter of Mother Vincenza, the head of the convent. She is closed up in a dark attic. Towards the end of the film, the horrific events reach the climax. Mother Vincenza murders Elisa. She herself pays for Elisa's death with her own terrifying death. Father Valerio, completely destroyed, loses his mind. Convent life seems to have returned too normal: there is a new Moth-er Superior, another Spiritual Father. But... Mother Vincenza's spirit, condemned to Hell, returns...