In rural Pennsylvania, a young girl screams for help in a rural meadow, her leg caught in an animal trap. A group of children, along with an older woman they call Mama, arrive, and one of the boys, Abraham, knocks the girl unconscious; Mama claims that the girl is actually a demon who has taken human form. Later, the children chant a Satanic prayer over the girl at the behest of their mother, and one of the children, Cynthia, proceeds to brutally stab her to death with a dagger.Years later, teenager Nancy Johnson (Melanie Verlin) runs away from her home after her abusive and alcoholic stepfather Bert (Lawrence Tierney), a police officer, attempts to rape her. While hitchhiking to her sister's home in San Francisco, she is picked up by two benevolent young men, Hank (Charles Jackson) and Tom (John Hall). In the backwoods, they pick up a Baptist preacher (Bob Johnson) and his adult daughter, Sandra (LaChele Carl), who they drop off at a cemetery to visit the grave of the preacher's wife. Sandra says a prayer and heads back toward their house; her father remains, and is stabbed to death by a man with a machete shortly after. Later, Sandra finds her father's corpse on their doorstep, and is murdered by the man with the machete.At a local bar, Tom, Hank, and Nancy encounter racist locals who refuse to serve them because Hank is African-American. Short on money, they steal groceries from a small market and are chased by two local police officers. They lose the police, and drive onto a dirt road into the woods, where they witness the murderer carrying Sandra's corpse (covered in a sheet) into the woods. The three find a spot to camp overnight.In the morning, Nancy goes for a walk, and returns to the campsite to witness two police officers, Luke (Greg Besnak) and Abraham (John Amplas), arresting Hank and Tom, accusing them of murdering a local woman (presumably Sandra). They execute both of the men, and then pursue Nancy, who flees into the woods. She comes across a farmhouse, and inside finds a teenage girl, Cynthia (Robin Walsh), playing cards. She asks for a phone, and is directed to another room; when she enters, she finds the man she, Tom, and Hank saw earlier (whom she comes to find is named Cyrus) dismembering two men. She is confronted by the two police officers, who lock her in an animal cage next to another victim, Gwen Davis (Amy Brinton). In conversation, Gwen recounts Luke and Abraham's murder of her sister and two police officers the night before, and then stealing their uniforms.Luke, Abraham, and Cyrus return to the campsite and burn the bodies of Hank and Tom as well as the corpses of the preacher and his daughter. Later, Luke goes upstairs and has a conversation with his dead mother, a decomposed corpse the family keeps in a bed. The next day, he and Abraham kidnap teenager Sharon from her backyard and murder her boyfriend, who tried to rescue her.Meanwhile, Bert goes to a local police station to report Nancy missing. Earlier, he had promised his wife Harriet (Doris Hackney), Nancy's biological mother, to find Nancy after noting she had been away from for an unusually long time.At the farmhouse, the family conduct a Black Mass at midnight and sacrifice Sharon in the name of Satan, as Nancy and Gwen watch from their cages. Nancy prays to God as they slit Sharon's throat before feeding her blood to their dead mother, attempting to resurrect her. They drive Sharon's body to a field the next morning and begin digging a shallow grave, an event witnessed by Bert, who is out searching for Nancy; he overhears them discuss sacrificing Nancy and Gwen on Easter Sunday.Later, while Cynthia sacrifices Gwen at midnight, Nancy recites the Lord's Prayer, and Luke drinks Gwen's blood. After the Black Mass, Luke prepares to bring Gwen's body outside, but is accosted by Bert, who clobbers him. He then holds Abraham and Cyrus at gunpoint, forcing Abraham to retrieve Nancy. Just as Nancy is brought outside, Cynthia attacks Bert, stabbing him to death in the back. As he collapses, he fires his gun, shooting both Cyrus and Abraham. Nancy hides in the barn where Cynthia chases after her, not knowing exactly where she is concealing herself. However, without warning, Nancy jumps out from behind her (seemingly almost out of nowhere) and in an expeditious act of revenge for the murder of her stepfather, manages to gain the upper hand, then proceeds to slit Cynthia's throat with a sickle.Luke regains consciousness, but Nancy is to quick to react and subsequently pours gasoline on the ground then lights him on fire. Nancy watches helplessly with satisfaction and reassurance as he burns to death while simultaneously screaming in agony. Severely traumatized by the whole ordeal, tears of both relief, anguish and despair begin to uncontrollably roll down Nancy's ashen face as she sighs to herself while realizing that the blood-curdling nightmare that she won't soon, or most likely ever forget is finally over. Knowing that her life will never be the same again, she presses her back up against the wall of a nearby wooden shed, and then looks in the direction of the camera with an incredibly forlorn look on her face until the credits begin to roll.