Four Flies on Grey Velvet () is a 1971 giallo film written and directed by Dario Argento. The film concerns Roberto Tobias (Michael Brandon), who accidentally kills a man and is then tormented by someone who witnessed the event. The film was an Italian and French production between the Rome-based company Seda Spettacoli and the Paris-based Universal Productions France.
Plot
Roberto Tobias, a band drummer, is being followed by a suspicious figure. He chases and confronts the stalker, who pulls a knife; in the following struggle, Roberto accidentally stabs and apparently kills the man. A masked figure snaps several photographs as this happens. In the ensuing days, Roberto receives threatening letters about his killing the stalker, Carlo Marosi.
At home that night, Roberto is ambushed by the masked individual, who tells him they are not finished with him before knocking him out. The maid, Amelia, witnesses this from the shadows. When Roberto's wife Nina returns home, he confesses everything to her but refuses to go to the police since he will be arrested for Marosi's murder. Amelia, who now knows the masked figure's identity, tries to blackmail them but is killed by them in a park. Despite Roberto's reluctance, Nina's cousin Dalia arrives to stay with Nina and Roberto.
Elsewhere, Carlo Marosi is still alive: his confrontation with Roberto was staged with a retractable knife. Marosi is working for Roberto's tormentor. Unnerved by Amelia's murder, Marosi tries to back out of their arrangement, but instead, the mystery figure kills him.
Roberto hires Arrosio, a flamboyant detective, to identify his tormentor. When Roberto returns home, he finds Nina leaving. She tells him she will no longer stay in the house with someone stalking them. Roberto resolves to remain. That evening, Dalia offers to take care of Roberto in the meantime, and the two start having sexual trysts after Roberto makes passes at her while in the tub.
After researching Roberto and Nina's history, Arrosio visits Villa Rapidi, a psychiatric facility. He speaks with a doctor about an unnamed patient diagnosed as a homicidal maniac. When this patient's father suddenly died, the psychotic symptoms inexplicably disappeared, and the patient was discharged. Later, while trailing the unidentified patient, Arrosio is ambushed and murdered with a poison-filled syringe.
Meanwhile, looking at family photos, Dalia notices a strange similarity between a photograph of Roberto and another one whose subject the audience can't see. The killer suddenly appears and stabs her to death. The police use optography to generate an image of the last thing Dalia saw before death but only get a blurry picture of four dark smudges against a gray background. The technician says the image looks like "four flies on gray velvet."
Knowing the killer will likely come for him next, Roberto waits with a gun in his darkened home. Roberto's friend Godfrey calls, but the line suddenly goes dead. Just then, Nina arrives home. Roberto urges her to leave for her safety, but he notices Nina's pendant necklace. It is a fly enclosed in glass, and as it swings, it gives the appearance of several flies on a grey background.
As Roberto realizes Nina is the killer, Nina grabs Roberto's gun and shoots him in the shoulder. Holding Roberto at gunpoint, Nina explains that her physically and mentally abusive stepfather committed her to the Villa Rapidi asylum. His death cured her condition but left her frustrated because she had wanted to kill him. Because Roberto bears a striking resemblance to her stepfather, Nina decided to torment and murder Roberto as a surrogate for him. She married him and planned the elaborate, cruel game she had played with him. Nina repeatedly shoots Roberto, but Godfrey arrives, distracting Nina so that Roberto can knock the gun from her hands. Nina speeds away in a car, but she crashes into the back of a truck. The truck's rear bumper decapitates her, and the car explodes in a mass of flames.