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