Daniela Neseri (Annik Borel) lives with her wealthy industrialist father, Count Neseri (Tino Carrero) in his secluded villa. Daniela was raped several years earlier and has developed an extreme phobia of men. When she finds a picture of an ancestor whom she greatly resembles, she becomes plagued by nightmares of herself becoming a werewolf and killing a man during medieval times. Count Neseri consults a psychiatrist (Elio Zamuto). The psychiatrist informs him that Daniela has become possessed by the ancestor's spirit and thus possibly could become a werewolf herself because lyncanthropy has been "proven."Daniela's sister, Elena (Dagmar Lassendar), returns from her studies in America, bringing her fiance, Fabian (Osvaldo Ruggieri). Fabian looks exactly like the man Daniela kills in her dreams. That night, she watches Elena and Fabian make love. Aroused but appalled, she rushes out of the house. She is confronted by the spirit of her ancestor, who tells her that "the circle has been completed." Fabian follows Daniela into the woods. She seduces him, but when he begins to make love to her, she rips his throat out with her teeth and dumps the body in a ravine.Driven mad by what she has done, Daniela is institutionalized. Because Daniela rages at anyone she sees, including her sister, the psychiatrist insists she be restrained at all times. But when another patient, a nymphomaniac (Giuliana Giuliani), tries to seduce her, Daniela frees herself, kills the woman with a scalpel and escapes the hospital. When she spies a couple making love in a barn, she waits until the man leaves and then kills the woman (Maria Renata Franco). The next day, she steals clothes from a housewife. The housewife takes the bloody hospital gown to the police, who recognize the connection to the dead woman in the barn -- and to the death of the Fabian. Inspectors Modica (Frederick Stafford) and Arrighi (Andrea Scotti) talk to Count Neseri and the psychiatrist, both of whom warn the policemen about Daniela's psychosis. Elena overhears the police say that Daniela is suspected in Fabian's death. She announces her hatred for her sister.After ripping out the throat of a man who tried to rape her, Daniela is found cowering at the side of the road by stunt man Luca Mondini (Howard Ross). He is unlike other men -- both passionate and compassionate. They fall in love and move in together. But one night while Luca is away, three men break in and rape her repeatedly. Luca returns and, in a brutal fight, is killed. The next day, Daniela gets her revenge, killing all three rapists. In investigating Luca's murder, Modica and Arrighi learn that Luca and Daniela had been living together. When Arrighi admits that he has been having nightmares about Daniela trapping him in the Forest of Solace, Modica realizes that is where they might find Daniela.He is right: Daniela, now almost feral, has a campsite there. Modica and Arrighi lead other police officers and medical personnel to the Forest, where they find Daniela dancing behind a wall of fire. As Modica watches, Daniela is captured, to be taken to a mental institution, where she will later die. Count Neseri will commit suicide.