The movie begins with a serene forest landscape in 14th Century Italy, where Sister Fernanda, played by Aubrey Plaza, is seen leading a donkey back to her convent, despite the sweltering summer heat while donned in heavy winter attire. Upon her return, she encounters Sister Genevra, portrayed by Kate Micucci, who questions her choice of clothing and the repeated escape of the donkey, leading to an argument between the two.
As they make their way toward the convent's living quarters, they pass the groundskeeper, who greets them cheerfully. In a fit of rage, the sisters hurl insults at him, as they have repeatedly told him to stay silent and avert his gaze. Their anger escalates, resulting in a comical vegetable and tool assault on him.
Meanwhile, in a nearby castle, Lord Bruno, characterized by Nick Offerman, is dining with his wife, Francesca, played by Lauren Weedman. During dinner, he drones on about financial woes and conflicts, annoying Francesca, who counters his monologue with sharp sarcasm. Her glances toward Massetto, a servant portrayed by Dave Franco, suggest a secret affair between them.
Later that night, following an intimate rendezvous, Francesca expresses her disdain for her husband’s tedious nature. Their flirtation continues until they are nearly caught by Lord Bruno. Massetto narrowly escapes through a window, but not before Bruno, suspicious of his servants, attempts to identify him by cutting off a lock of hair and proclaiming, "Now I will know who you are in the morning."
The following day, the furious Lord Bruno's anger peaks when he discovers his wife’s indiscretions. In retaliation, he instructs his guards to punish Massetto. Meanwhile, back at the convent, the diligent Sister Alessandra, portrayed by Alison Brie, embraces her duties of weaving and sewing while Father Tommasso, played by John C. Reilly, plans a trip to market with her handiwork. The tension further rises among the sisters, as Fernanda and Genevra express their concerns regarding Alessandra’s unfair advantages due to her father's financial contributions to the convent.
In a twist of fate, Massetto inadvertently crosses paths with Tommasso—who is inebriated and has lost his fabrics to the river—leading them to hatch a plan for Massetto to assume the position of the mute and deaf groundskeeper in order to avoid the wrath of the sisters. Their scheme seems to work initially, as Massetto finds himself amidst curious and wary glances from the sisters.
A comedic night unfolds when Massetto encounters various escapades, including the unexpected arrival of his friend, who introduces a potion concocted from belladonna that leads to wild nights filled with mirth and forbidden encounters. The lines between friendship and desire blur as the sisters drunkenly experiment with their newfound power over seduction, culminating in a series of intertwining liaisons.
As the Bishop, played by Fred Armisen, arrives to inspect the convent, chaos ensues, leading to horrifying truths being revealed, drastic confessions, and escalating confrontations. The sisters grapple with their feelings of betrayal and guilt, culminating in a climactic confrontation that lays bare their hidden sins.
The unfolding events lead Massetto back to imprisonment at Lord Bruno’s castle, where he faces threats from the guards and a cruel outlook from the lord himself, who revels in the circumstances that surround his wife. However, armed with determination, the sisters unite once more to rescue Massetto, leading to an escape filled with surreal twists.
As the story intensifies, love and secrets intertwine among the sisters, leaving them grappling with their own identities and loyalties. In the film’s closing moments, the characters seek solace in the woods, reaffirming their bond while the film captures a lasting sense of mystery, culminating in an abrupt yet powerful conclusion.
