Your Vice Is a Locked Room and Only I Have the Key

Oliviero Rouvigny, a washed-up alcoholic writer, lives in a creaking villa in Teolo. He brutalizes his wife Irina and their maid Brenda, and hosts debauched parties for local hippies. He remains obsessed with his cat Satan and with his late mother's dress Esther wore to portray Mary Stuart.

Fausta, Oliviero's mistress, is found murdered and Inspector Farla questions him. Oliviero claims he was at home, with Irina providing a reluctant alibi, while Fausta's boss Bartello identifies Oliviero as a suspect. The case tightens around the writer.

That same night Brenda is attacked with a billhook and dies. Irina discovers the corpse, while Oliviero, visibly drunk, remains detached from the violence around him. The household's tension escalates into fear.

Terrified by suspicions, Oliviero walls Brenda's body up in the cellar and insists Irina discreetly clean his mother's gown. The murder remains hidden beneath the villa's walls.

The next day the Rouvignys collect Oliviero's visiting niece Floriana at a nearby train station, observed by a gray-haired man lurking nearby. The quiet is punctured by the sense of unseen eyes on them.

The gray-haired man delivers Esther's dry-cleaned gown to Irina, enraging Oliviero. In a rush of jealousy and fear, Oliviero locks Irina in a closet, planning to subject her to Satan's cruelty.

Floriana frees Irina from the closet and the two women share a secretive, charged moment. Floriana teases Oliviero about his attraction to her and hints at an incest rumor that shadows their family dynamic.

A prostitute named Giovanna is murdered by an unknown killer, and Giovanna's madam later kills the attacker, revealed to be Bartello, who has escaped a psychiatric hospital with a new identity. The criminal web widens as Bartello's past resurfaces.

Floriana begins dating motorbike racer Dario. After he is forced to drop out of a race, Dario and Floriana have sex in an abandoned loft while Oliviero spies on them from afar.

Mrs. Molinar witnesses Irina stabbing out Satan's eye with scissors after Satan kills several of Irina's pet doves. The cruel escalation of violence marks a turning point in the household's power dynamics.

Oliviero discovers Floriana wearing Esther's gown. Floriana reveals she knew he witnessed her with Dario, and the two exchange a tense, knowing kiss as their dangerous liaison continues.

Floriana informs Irina about the encounter and Oliviero's growing urge to murder Irina and hide her body in the cellar. Irina eavesdrops on pillow talk and later confronts Oliviero, beating him in a tense showdown.

Irina kills Oliviero at his desk with scissors, ending his reign of terror. Floriana secures Esther's jewelry and helps hide Oliviero's body in the cellar; the two women briefly bond amid the carnage.

Walter, the gray-haired lover, enters the villa and types vendetta on Oliviero's typewriter, revealing himself as Irina's accomplice. He orchestrates the others' deaths and is later sabotaged by Irina, who pushes him off a cliff after he retrieves Esther's jewels. The next day, Inspector Farla arrives and, guided by Satan's meow, the police discover Oliviero's body in the cellar beside Satan.