After wrapping up a recording session with his garage band, drummer Roberto (Michael Brandon) follows and confronts a mysterious stranger who has been stalking him to an abandoned theater where Roberto impulsively stabs him. A grinning puppet-like figure takes photos of the attack from a mezzanine box, which arrive in an envelope at Roberto's home the following day. It appears that he is being blackmailed, but it's not clear from whom or why. Suspects include a club-footed neighbor and various friends. After Roberto confesses to the stabbing, his housekeeper discovers the killer's identity, is murdered, and an increasingly paranoid Roberto sends his wife, Nina (Mimsy Farmer), out of town. He eventually tracks down the man he stabbed with the help of a flamboyant detective (Jean-Pierre Marielle) and colorful transient friend Godrey (Bud Spencer), but both the man and the detective are killed. Roberto's cousin Dalia (Francine Racette) visits and, against their better judgment, they begin a passionate love affair. Elsewhere, the police use a special camera that can capture the final image a murder victim sees off their eyeball; this technique is used to track down the real killer.