Plot Summary2: Roberto Tobias (Brandon) is a drummer in a rock band who has noticed a man following him for the last several days. Angered by this, he confronts the stranger in an abandoned theater to find out what he wants. The man claims he does not know what Roberto is talking about, and pulls a switchblade. The two struggle, and Roberto accidentally stabs the man, who falls into an orchestra pit, lifeless. To make matters worse, someone in a bizarre puppet mask has been hiding in the upper wings of the theater, and takes incriminating photos of Roberto holding the bloody knife. Roberto flees, but the next day he receives the dead man's ID in the mail. It becomes apparent that the masked figure has no interest in going to the police, and instead wants to drive Roberto mad with fear and paranoia. But why?

Music
Deep Purple was considered for the score but this film was scored by the world famous composer Ennio Morricone noted for his scores in Sergio Leone films (in which Argento co-wrote Leone's Once Upon a Time in the West) and had previously worked on Argento's The Bird with the Crystal Plumage, but due to disagreements would not later work with Dario Argento again until the scoring of The Stendhal Syndrome (1996). They collaborated later on the The Phantom of the Opera (1997).

Technology
Within a major point, as a plot device, a technique was used within the movie to give a clue to the killer, where up to a few hours after death the image of the last image seen is burned into the retina. Argento was originally reluctant feeling it too out-there for the giallo genre, but was later convinced when he was shown by Carlo Rambaldi how it would look in the film.Predating Argento's own Stendhal Syndrome, The Matrix, and numerous Hong Kong films, a slow motion bullet effect is used in the film.To film a car crash, a camera that could produce a triple digit amount of frames per second and twelve cars were used to get the effect shown in the film.

Lack of availability
This film is the third in Dario Argento's Animal Trilogy in the early 1970s that started with The Bird with the Crystal Plumage and The Cat o' Nine Tails. It currently is the only film of his that is unavailable on VHS or DVD in a legitimate version, either domestically or internationally with the exception of the long out of print obscure French VHS. Digital bootlegs show up on P2P sites with poor quality in image and sound. The rights to this film (at least in America) are owned by Paramount, which has chosen not to release it. Copies of varying quality are available from numerous online conversion sources. Recently though, a German PAL DVD has surfaced and was released on December 20th, 2007 from an outfit called Retro Films. This unofficial release offers a widescreen anamorphic transfer, as well as Italian, English, and German audio options and optional German subtitles. An array of trailers and alternate credits/ending are included. The print is from a slightly cut English theatrical copy and inserted footage from a VHS copy provides the cut footage to bring the running time up to 97 minutes..(here)