The film was released in Italy and through most of Europe without any reported censorship problems, but was classified and banned as a Video Nasty in the United Kingdom. Its theatrical distribution in the United States was delayed until 1984, when it was released in a heavily-censored version under the title Unsane.
Franciosa stars as Peter Neal, a American writer of violent mystery novels. In Italy to promote his latest work, he is accompanied by his literary agent Bullmer (Saxon) and his assistant Anne (Nicolodi). He is unaware that he is also being followed by his embittered ex-wife Jane (Lario).
Prior to Neal's arrival in Rome, a young woman is brutally slashed to death by an unseen killer. The murderer sends Neal a letter informing him that his books have inspired him to go on a killing spree. Neal is soon contacted by the police, who put Detective Giermani (Gemma) in charge of the investigation.
While the killings continue, Neal notices that TV interviewer Cristiano Berti (John Steiner) appears to have an unusually intense interest in the novelist's work.
Just when you think you know who the killer is, he is violently killed himself.
This film provides examples of:
- Accidental Murder: In the end, Anne accidentally kills Neal when she pushes a statue and a sharp piece falls off, transfixing his chest and pinning him to the wall — a death that is as accidental as it is a merciful stroke of luck, as it prevents him from stabbing her as well.
- The Alibi: Deliberately invoked by one of the killers. Neal uses Berti's killings, which happened before Neal came to Italy, to throw suspicion off himself as he plans the murders of Berti, his agent, his wife, and his secretary. He advises the police that, in his opinion, all of these killings are being committed by the same person — and since he wasn't in the country yet, that rules him out, right?
- An Arm and a Leg: Peter's ex-wife Jane has her hand chopped off with an ax right before being killed.
- Angry Guard Dog: Maria is frightened by one. She then foolishly aggravates it further, providing a chase scene that leads her to the killer's basement.
- An Axe to Grind: Primary tool for murder during the latter part of the film.
- Anyone Can Die: By the end of the movie, everyone except Anne is dead.
- Ax-Crazy: Both Cristiano Berti, who was inspired by Peter Neal's books into acting into his maniacal homophobic desires, and then Neal himself, who was inspired by Berti's getting inspired by his books.
- Big Bad: Subverted with the reporter Cristiano Berti, who indeed kills the first few victims but is killed by Peter Neal who then takes over as the Big Bad.
- Big Bad Wannabe: Cristiano Berti, who was indeed the murderer of the first few victims, but is killed off by Peter Neal, the actual Big Bad.
- Daylight Horror: Argento and cinematographer Luciano Tovoli shot most of the film in bright or brightly lit locations, even at night. White is the predominating color, which makes for an Ironic Episode Title, because "Tenebre" is literally Italian for "darkness".Dario Argento: Suspiria was a great explosion of lights and colors, but here I wanted to do a very cold kind of film, like ice.
Luciano Tovoli: There's no shadow in which to hide, not even for the viewer... If I could have done it, I'd have lit the theater too.
- Decoy Protagonist: Initially, the film follows Peter Neal. However, after Neal takes over as the Big Bad, the climax follows Anne instead.
- Disc-One Final Boss: Christiano Berti is the killer at first, but is himself killed by protagonist Peter Neal about halfway through. Neal takes over as the killer afterwards.
- Downer Ending: Peter is revealed to be the killer and after killing the inspector among others, he lastly attempts to kill Anne only to get impaled to the wall. While Anne survives, she is the only survivor, and the last shot of the movie is of her in a violent screaming fit of hysterics, sealing the fact that she is going to be traumatized for the rest of her life at the very least.
- Epic Tracking Shot: A truly spectacular one going up and around of multiple floors of a building leading up to a double murder.
- Establishing Character Moment: Peter Neal's rather cavalier attitude toward his own success is revealed at our first sight of him. He owns a Rolls and pays a chauffeur, but instead of being driven to the airport he bicycles behind his car all the way; he retrieves his luggage from the car boot, puts his bike in it, and is next seen hurriedly changing from his tracksuit into a business suit in the airport men's room. All this seems to suggest it's not the lure of money and fame that keeps him writing; he has other concerns. Like the opportunity to exorcise his own personal demons.
- Greater-Scope Villain: Due to the revelation that Peter Neal was the killer for the later act and that his literary work (which in turn inspired Disc-One Final Boss Berti to go on a murder spree) stems from his Dark and Troubled Past as a teenager who killed a girl out of revenge for the humiliation he suffered, Neal acts as this for Berti in the first half of the film.
- Impaled with Extreme Prejudice: This happens to the killer in the climax.
- The Killer in Me: Peter Neal has always had repressed feelings of misogyny and violence. He attempts to exorcise them in his books, but once somebody starts killing due to his books, he loses any control he had, kills the actual killer and embarks on a spree of his own.
- Metafictional Title: Tenebre is Neal's latest book.
- Ms. Fanservice: The lesbian reporter Tilde's girlfriend, who is naked for almost entire duration of her role.
- One-Word Title
- The Oner: The three minute shot that pans up and over Tilde's house.
- The Quincy Punk: While waiting for Jane to have lunch with her, Bullmer notices two punks hanging around.
- Red Herring: All male characters, but particularly John Saxon as a sleazy agent. Subverted with Berti — he is the killer in the first few murders we see or hear about but gets killed by Neal halfway through the film.
- Sadist: Peter Neal himself, who murdered a girl in his youth to vent his sexual frustrations, and starts killing again when the new murders awaken his bloodthirst.
- Slashed Throat: This is how the first victim dies.
- Two Dun It: Berti for the first half of the movie, Neal for the second.
- Vengeance Feels Empty: It didn't take much time for Neal to stab the girl who sexually humiliated him to death. It also evidently didn't provide him with any solace either, as many, many years later his obsessive hatred remained as strong as ever, festering in the depths of his soul and resurfacing during the most opportune moment.
- Video Nasties: It was one of the 39 prosecuted films.
- Villain Protagonist: Peter Neal turns out to be a misogynistic murderer whose bloodlust remained dormant for many years, which made him both appear and believe himself to be gentle... until it comes back with a vengeance.
- Your Approval Fills Me with Shame: A variation. Berti asks Neal, with an excited voice, if he agrees with the view of the killer in the novel that homosexuals are disgusting and disposable perverts. A visibly disturbed Neal comments that the novel's main character is a psychopath. Considering that Berti is Ambiguously Gay, it adds a subtext and motivation, too.