A famous Italian-American writer of horror novels goes to Italy to spend a few days in an old house on the coast. The history of the house begins to manifest itself with hallucinations, which the writer notes as ideas for his novel. He then meets some locals who tell him the story of a cult who came to the house in the 1970s to build a temple dedicated to Satan.

Rome is shattered by a series of gruesome murders that paint the Eternal City deep red. The suspicion grows that these atrocious crimes are connected with the return of one of the most heinous serial killers of our time - Karl the Butcher.

During an analytic session, a psychologist recommends that one of her patients be admitted to a specialist clinic, but this decision unleashes the mysterious individual's latent madness. Abandonment is the key to his delusion, which will lead him to kill once again, as he had done in the past with his first, lost love. So, after disposing of the analyst's body, he decides to continue the "therapy" alone with the aid of a small video camera, recording his emotional states in a hallucinatory crescendo.