In Sicily in 1486, a mob of villagers torture and crucify five nuns, suspected of witchcraft, in a chamber beneath their convent.
At a seance in Toronto in 1990, Liza (Meg Register) has a vision of the crucified nuns and falls screaming onto the floor. Several months later. Liza and Professor Evans (Brett Halsey), a respected archaeologist and her former professor, lead a survey team to Ancient Greek ruins on a site near the small town of Santa Rosalia, Sicily. The locals, including Porter (Al Cliver) and Turi (Lino Salemme) tell them to avoid the beautiful but ominous ruins of a monastery that overlooks the dig. Although Professor Evans reminds her that she should avoid any involvement with the supernatural after the seance in Toronto, Liza is fascinated by the morbid rumors about what had happened in the monastery.
Ignoring Turi's angry rebuke, Liza enters the monastery crypt. Convinced that there is another chamber behind a wall, she uses a pick-axe to break into the cavern containing the charred remains of the five nuns. But when Liza tells Professor Evans what she has found, he angrily tells her to forget she saw anything.
Soon, supernatural murders begin to take place. Porter is killed on his boat by a harpoon gun-wielding spectral nun. Two members of the archaeological team, Sean (Grady Thomas Clarkson) and Kevin (Pascal Druant), are lured into the ruins by enticing female voices and then killed when they fall through a weak floorboard and land into a pit of metal spikes. Eventually, Inspector Carter (Lucio Fulci) from Interpol arrives to investigate the deaths.
Meanwhile, Liza pursues her investigation into the monastery She meets with a strange-looking woman (Carla Cassola) who tells her about what happened at the ruins centuries ago. The nuns practiced witchcraft and held orgies there as well. Local youths wound be invited there for sex, then murdered as they reached orgasm. The nuns would drink their blood in a satanic frenzy. If any one of the crazed nuns would become pregnant, they would carry their unwanted babies to full term, then throw the newborns onto a fire. After Liza leaves, the old woman is clawed to death by her pet cats.
Professor Evans puts suspicion on Turi the butcher, who has openly threatened violence against the archaeolgists. But that evening, Turi is killed in the freezer of his meat shop. Inspector Carter finds a piece of torn clothing clutched in Turi's right hand which apparently belonged to his killer. Now under suspicion himself for Turi's murder, Professor Evans decides the dig will be abandoned, but Liza, acting more and more strangely, refuses to leave.
The next morning, the enraged townspeople attack the haunted ruins, Professor Evans tries to get his team clear. But he realizes that Liza and Robby, the young son of two team members, are missing. Robby has been kidnapped by a white-robed, faceless nun. He manages to escape but, just outside of the camp, sees his father ripped in two by a hidden trap.
Professor Evans pursues Liza, who is dressed in a white robe and possessed by the spirits of the evil nuns, into the ruins. She stabs him in the stomach and then disappears like a ghost. The mob of townspeople charge into the hidden chamber. Liza reappears, foaming at the mouth on one of the crosses. The mob sets her and all the skeletal remains of the nuns afire. The wounded Professor Evans staggers into the cavern, pushing the mob members out of his way, to see Liza materialize at the foot of the burning crosses, no longer possessed but dead.Brett Halsey: Paul Evans
Meg Register: Liza
Lino Salemme: Turi De Simone
Christina Englehardt: Susie
Pascal Druant: Kevin
Grady Thomas Clarkson: Sean
Ettore Comi: John
Carla Cassola: la medium
Michael Aronin: Andy
Al Cliver: Porter
Francesco Cusimano: Robbie
Lucio Fulci: Inspector Carter