It is based on real-life events related to Marianna de Leyva, better known as Sister Virginia Maria, "The Nun of Monza", whose story was made famous by Alessandro Manzoni's novel The Betrothed.

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.

Disgusted by Virginia's hypocrisy, Caterina threatens to expose the nun's affair with Osio and the existence of their illegitimate child.

He writes a self-serving letter to Cardinal Borromeo and seeks refuge with a friend, who 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.

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.

Tim Lucas of Video Watchdog described Devils of Monza as "an elegantly crafted little gem...exquisitely photographed by Romano Albani [with] one of Pino Donaggio's most beautiful scores," and singled out Myriem Roussel's performance for praise: ...what is most lingering about the picture is what lingers about the films Roussel made with Godard: the devotion it pays to her Renaissant loveliness, which somehow looks as much at home in a nun's habit as in the basketball uniform she sports in Hail Mary.

There's a scene in Sacrilege where Sister Virginia, awakening to her sexuality under the smouldering, corruptive gaze of neighboring nobleman Giampaolo Osio (Alessandro Gassman), looks into a mirror and pulls her habit away from a cascade of long auburn hair.

The effect is nearly breathtaking... What makes this moment so powerful is how, in the space of these few frames, Roussel's expression subtly morphs from timid curiosity to combined arousal and sorrow -- she tears her habit like a hymen -- and then from awe at her mirror's disclosure of her sensuality to a final expression that shows contempt for her vanity as she feels herself empowered by it.

It is the moment of Sister Virginia's emergence as a complete, sexual being, body and soul, and by this point in the movie, we feel our heart breaking for her as it also pounds for her.