Set in a nunnery in early-17th century
Monza, Northern Italy, the film depicts the clandestine sexual relationship between a beautiful young nun of noble birth, Sister Virginia Maria de Leyva, and a rakish local aristocrat, Gian Paolo Osio, whose estate is adjacent to the nunnery. Osio is attracted to the proud, haughty, and sexually repressed Sister Virginia, and attempts to
court her with letters and charms provided by his lecherous friend, corrupt local priest Father Paolo Arrigone. Osio gains access to the nunnery via counterfeit keys provided by a local
blacksmith. Inside the nunnery, Osio
rapes Virginia in full view of her appalled roommates, Sisters Benedetta and Ottavia. The relationship between Virginia and Osio becomes consensual and the pair engage in a series of increasingly passionate trysts, even as Virginia presents to the other nuns and the outside world the appearance of piousness and celibacy. Virginia's subordinates and confidants, Sisters Benedetta and Ottavia, become aroused by Virginia and Osio's lovemaking, and engage in
mutual masturbation as they watch Osio perform
cunnilingus on Virginia. Virginia alternates between gratifying her lust and feeling tremendous guilt for her sins. She also becomes fearful that her improper relationship with Osio will be exposed. Later, when Virginia falls ill and bedridden, the lustful Sister Benedetta takes advantage of the situation and confesses to Osio the love she claims she and Sister Ottavia have for him. A weakened and distraught Virginia cries as she watches Osio, Benedetta, and Ottavia
have sex. Osio's friend, Father Paolo, imposes himself further into the growing scandal by molesting one of the nuns, Sister Candida. Virginia falls pregnant by Osio and gives birth in secret to an illegitimate child. A rebellious
novice, Caterina, runs afoul of Virginia's discipline. Disgusted by Virginia's hypocrisy, Caterina threatens to expose the nun's affair with Osio and the existence of their illegitimate child. Virginia has Caterina locked in a barn and Osio later murders her and disposes of her body. Father Paolo decides to blackmail Osio. The convent is rocked by increasingly scandalous rumours, and suspicion surrounding Caterina's disappearance, all of which derail Virginia's attempt to become nunnery's
Mother superior. The situation escalates when
Federico Borromeo,
cardinal and
Archbishop of Milan, orders an official investigation. Virginia is arrested and questioned by Church authorities. A desperate and increasingly murderous Osio sets about to silence the accomplices who can incriminate him. He kills the blacksmith who forged the keys that allowed him to infiltrate the nunnery. He then persuades Sisters Benedetta and Ottavia that they are in danger and need to flee with him. Away from the nunnery, Osio attacks the two nuns and leaves them for dead. The wounded pair are later discovered and questioned. Osio becomes a wanted fugitive with a price of 1000
scudi on his head. Although he loves Virginia, Osio refuses to accept responsibility for his part in her downfall. He writes a self-serving letter to Cardinal Borromeo and seeks refuge with a friend, the aristocrat Cesare Taverna. Taverna betrays Osio and has him stabbed to death. The confessions and testimony extracted by the investigator appointed by Borromeo are sufficient to find Virginia, her collaborators, and Father Paolo guilty. Virginia admits to her sins but claims she did so under diabolical influence and always practised self-admonishment. Virginia is sentenced to lifetime solitary imprisonment in a small stone cell. En route to her cell, Virginia catches a glimpse of Sisters Benedetta and Ottavia, also punished for their complicity in her crimes. A closing caption states Virginia was released after serving 13 years of her sentence and impressed Borromeo with her repentance, which had taken on an entranced, mystical quality. Surviving
the Plague, she eventually died at the age of seventy-four. == Cast ==