In 1985, Enid Baines works for the British Board of Film Classification during the height of the Video Nasty controversy. Enid’s co-workers call her “Little Miss Perfect” due to her strictness in recommending that violent content be cut or banned. While Enid is having dinner with her parents, they discuss the disappearance of Enid’s sister Nina when the two were little. Enid’s parents have since declared Nina legally dead, but Enid is convinced that her sister is still missing.
Shortly after a man murders his wife and children, a tabloid newspaper links the killings to a film Enid had rated several months prior, naming her as the censor who approved it. Enid starts to receive phone calls threatening and insulting her on a regular basis. One day, Enid is approached by Doug Smart, a film producer who claims that a veteran horror director named Frederick North has personally requested that she screen one of his old films, Don’t Go in the Church. During the screening, Enid notices that events depicted parallel her memories of her sister’s disappearance.
Investigating North further by acquiring a copy of one of his banned films, Enid notices that the film’s lead, Alice Lee, bears a resemblance to her missing sister. Enid soon becomes obsessed with meeting North, believing that Lee is her missing sister, and needs to be saved from the exploitation film industry. When Enid visits Smart, hoping to learn North’s whereabouts, he tells her that North is making a sequel to Don’t Go in the Church near his home, and attempts to have sex with her. Enid rejects Smart, causing him to become more aggressive before Enid pushes him back, tripping and accidentally impaling him on a film award. Smart dies as Enid stares in shock, unable to process what has happened.
After stealing North’s address from her work, Enid finds the set of North’s latest film, where he and the crew assume her to be an actress. During a climactic scene, Enid kills an actor named Charles with an axe, thinking that he was going to hurt her “sister”. A terrified Alice flees from Enid as she begs for Alice to “please be her” before collapsing in the woods. A remote control appears in Enid’s hand, and she presses a button.
Enid is awoken by a seemingly happy vision of her sister, thanking Enid for finding her. Nina and Enid leave the woods and drive to their parent’s home. During the drive, the car radio announces that all violent films have been banned, crime has been eradicated, and unemployment no longer exists. Enid’s fantasy is sporadically interrupted, revealing that she has kidnapped Alice, who is begging Enid’s parents for help as Enid smiles.