Isabella, Francesca Ungaro, one of many beautiful models at Christian Haute Couture, a Roman fashion house, is strolling the estate’s grounds at night when a masked assailant—wearing a white featureless mask, a black fedora, and a trenchcoat—strikes, killing her in a chilling act of stealth. Inspector Silvestri begins the investigation, interviewing Massimo Morlacchi Cameron Mitchell, who co-manages the salon with the recently widowed Countess Cristiana Cuomo Eva Bartok. The inspector also questions Isabella’s ex-boyfriend, Franco Scalo Dante DiPaolo, an antique dealer, and uncovers that he is a cocaine user while noting that Isabella had been trying to help him kick his habit.
A diary emerges as a key clue, revealing that Isabella kept notes on the staff’s private lives and vices. One model, Nicole Ariana Gorini, discovers the diary and promises to hand it over to the police, but her coworker Peggy Mary Arden steals it during a fashion show. That very night, Nicole goes to Scalo’s shop to supply him with cocaine, only to be stalked by the killer and slain with a spiked glove. The killer rifled through Nicole’s body and purse searching for the diary, but it is nowhere to be found.
Meanwhile, Marco Massimo Righi, a nervous dresser with unrequited feelings for Peggy, visits her apartment offering protection, which she refuses. The killer drags Peggy away after a brutal confrontation and ties her to a chair, where Silvestri continues his interrogation via a tense sequence of questions. Peggy eventually tears off the mask and recognizes her attacker, who kills her by burning her alive in a furnace.
Silvestri gathers his suspicions and begins rounding up suspects, convinced the killer is a sexual deviant among the salon’s men. When Marco is implicated due to a visit to Peggy’s apartment, he tries to deflect onto Cesare Lazzarini Luciano Pigozzi—the dress designer who handles the house’s eavesdropping—only to suffer an epileptic seizure and be placed in the hospital, where his medications reveal a medical condition rather than impotence. As the round of arrests unfolds, Greta Lea Lander, another model, discovers Peggy’s corpse stashed in the trunk of her fiancé’s car, and the killer smothers her to death in that fiancé’s mansion. With Peggy and Greta dead, Silvestri releases the remaining suspects, and Morlacchi retrieves the same notebook he used earlier to question Peggy.
The two powerful figures, Morlacchi and Cristiana, later discuss the killings: Morlacchi admits to having killed Isabella, Nicole, and Peggy, while Cristiana confesses to murdering Greta to provide him with an alibi; the sensationalized, sexualized murder spree is revealed to be a smokescreen to hide their true motives. Isabella had learned of their earlier murder of Cristiana’s husband and had attempted to blackmail them.
Morlacchi urges Cristiana to commit one final murder to satisfy Silvestri’s theory, and she complies by killing a fifth model, staging the death as a suicide and leaving the trademark mask, hat, and coat scattered in the bathroom to direct suspicion toward the models. Cristiana prepares to flee when a loud knock comes at the door. In the ensuing escape attempt, she plummets from a second-story window.
Back at the fashion house, Morlacchi feverishly searches Cristiana’s desk for her jewelry, only to be confronted by Cristiana herself, who has come to realize that Morlacchi’s ambition was to inherit her fortune through their marriage. In a final, fatal confrontation, she kills Morlacchi. After summoning Silvestri, Cristiana collapses beside Morlacchi’s body, their scheme exposed and its bloody toll laid bare.
