A faceless man drives around Los Angeles, California, listening to a fiery sermon about sinners going to hell. “If it’s against the word of God, cut it out,” demands the preacher. The driver pauses at a corner, remembering the death of a teenage girl in a car accident, then stops at an apartment complex, where he lets himself into the apartment of Mrs. Andrews, a middle-aged alcoholic. When Mrs. Andrews asks why it has taken him so long to reply to her maintenance request, the faceless man pulls out a drill and kills her. He puts on a ski mask before leaving in search of another victim in the same building. Debbie, a young woman, steps outside her door and is knocked unconscious. The man drags her to a stairwell, where he bashes her head with a hammer, then carries her dead body back to her apartment. When Debbie’s friend, Maria, arrives and rushes over to the corpse, the man locks the door and kills Maria with a screwdriver. Later, an African-American couple finds the bodies and police detective Mark Jamison questions the couple about Mrs. Andrews. At the second crime scene, Sgt. Cameron questions a neighbor, who reports that Debbie moved in six months prior and that Maria came over often. Detective Jamison arrives and takes note of pornographic magazines with pictures of nude women spread out on a coffee table. He asks the owner of the building, Vance Kingsley, for a list of current and past tenants, but Kingsley insists he personally screened all applicants and cannot believe one of them could be the killer. The next morning, teenager Laurie Ballard gets ready for school as her mother, Joanne, sleeps in. Her older brother, Joey, complains he overslept and Laurie chides him for staying out all night. The next evening, a vain young woman named Dee Ann DeVore masturbates in a bubble bath as the faceless man secretly watches. When Dee Ann sees him, she runs for her life, but he shoots her multiple times with a nail gun, killing her. Back in the Ballard apartment, Laurie talks on the phone with her boyfriend. The killer breaks in, knocks Laurie unconscious, and kidnaps her. Later, Joey and Joanne come home wondering where Laurie is when they hear a neighbor’s scream. Running outside, along with other neighbors, they learn Dee Ann was murdered. Panicked, Joanne asks if anyone has seen Laurie. The next day, Detective Jamison asks Joey to account for his whereabouts the nights of the murders. Jamison says there is no evidence that Laurie was forcefully taken and suggests Laurie might have run away. Joey disagrees, insisting the murders and the kidnapping are connected. Frustrated, Joey declares he will investigate on his own. The next day, Joey visits one of the victim’s apartments and finds Kent Miller, the nephew of the building owner, Vance Kingsley. Kent, who was hired to clean the apartments, mentions that his cousin, Kathy Kingsley, died in a car accident a few years ago. Joey recalls she was a sophomore in high school just like Laurie, and asks for Kent’s help investigating his sister's kidnapping. Searching Dee Ann’s apartment, Kent deduces that a nail gun killed her when he finds several bloody nails in the wall. As Kent and Joey drive to Kingsley’s house to pick up painting material, Kingsley becomes angered by the commotion. He gives Kent cash and tells the boys to leave immediately, then watches from his kitchen window as he prepares a lunch tray. Kingsley brings the tray to the room of his dead daughter, Kathy, where Laurie is bound and gagged. He talks about losing his daughter and thinks God took her because she was pure. Kingsley believes the world is full of evil people, but if he kills them, good will prevail. He confesses to murdering the four women because they were sinners, then tells Laurie how much she reminds him of Kathy. With her gag removed, Laurie tries to convince Kingsley she is Kathy so he will let her go, but he puts the restraint back in her mouth. Later that evening, Kent returns and looks through the window to Laurie trying to chew through her restraints, but he runs away when Kingsley enters the room. The next day, Joey visits Kent as he paints Mrs. Andrews’ apartment. Detective Jamison arrives and mentions there was no forced entry in any of the murders, wondering how the killer conned his way inside. When Joey suggests that the killer might have an inside connection to the building, Kent looks worried, but Jamison does not take Joey’s theory seriously. On a hunch, Joey returns to Kingsley’s house and sneaks into the garage. There, he finds a toolbox and notices dried blood. When Kent arrives, Joey says he suspects Kingsley, but Kent insists Joey is wrong, grabs a buck of paint thinner, and throws it on Joey. Kent, declaring he must protect his family, throws lit matches on Joey and burns him alive. Meanwhile, inside the house, Kingsley and Laurie hear screams, but Kingsley says its just children playing outside. Calling Laurie “Kathy,” Kingsley promises to always protect her. As Kent confronts Kingsley about the kidnapping and murders, Kingsley tells Laurie that his nephew always protected Kathy from bad boys. When Kent confesses that he and Kathy were secret lovers, Kingsley is enraged. He and Kent fight and stumble into the kitchen, where Kent stabs Kingsley to death. Kent returns to Kathy’s room and unties Laurie, who thanks him for saving her. However, Kent rapes Laurie instead of calling the police, then tells Laurie that Joey died. Realizing that Kent killed her brother, Laurie reaches for a pair of scissors. Hours later, Laurie wanders the streets of Los Angeles in shock.