In Amityville, New York, the same town where Ronald DeFeo Jr. murdered his family in 1974, The Priest is shot to death in a confession booth inside his parish church. After the murder, the booth is removed and stored in the basement of the clergy house.
Twelve years later, Marvin David Stein and his wife Debbie Dawna Wightman buy the clergy house. The couple invite their three friends: Frank Kim Coates, Bill Anthony Dean Rubeš, and Abigail Cassandra Gava to help renovate. Debbie is immediately perturbed by the house and hears noises emanating from the basement, but Marvin dismisses her concerns. Debbie suffers nightmares revolving around the basement, particularly the confession booth. Marvin urges Debbie to note down her nightmares so he can psychoanalyze them. The next morning, Mrs. Moriarty Helen Hughes, the eccentric former church secretary, pays a visit.
Marvin and Bill investigate the basement, and Bill comes across the confession booth, among other artifacts from the church. After an outbreak of apparent poltergeist activity occurs throughout the house, the group all become convinced the home is haunted, with the exception of Marvin. To calm their nerves, they plan to go out for dinner at a local bar. Frank, suffering a migraine, remains at the house alone. At the tavern, Marvin speaks to two older men regarding the town's paranormal activities and feels it is nothing but a case of mass hysteria. The men bring up a boy murdering his whole family and possibly being possessed, and implying the house Marvin is currently in is likely possessed. At the same time, Debbie encounters Mrs. Moriarty again in the bathroom, where she obscurely rants and raves about the priest who once lived in the home.
The next day, Mrs. Moriarty again stops by the house, but is confronted by an unseen assailant and thrown down the basement staircase to her death. Her murder is inadvertently recorded on a video camcorder Bill left in the house. Meanwhile, Debbie has a disturbing vision of a man hanging from a tree in the front of the house. Police are summoned after Mrs. Moriarty's body is found, and a detective tells Marvin about her connection to the house; he also divulges that police identified the murderer of the priest, a local teenage boy, but that he hanged himself before he was apprehended.
Abigail is disturbed by the event and leaves. Marvin begins attempting to decipher Debbie's dream diaries, which Bill realizes consist of Latin exorcism writing. Meanwhile, Debbie suffers a nightmare in which she witnesses the truth of the priest's murder: He was shot to death by his illegitimate son, conceived during a sexual tryst with a female parishioner, who sought vengeance for being abandoned. She awakens and searches for Marvin, whom she finds dead in the confession booth in the basement. There, she is confronted by Frank, now possessed by the priest's illegitimate son. Meanwhile, police investigating Mrs. Moriarty's murder review the video tape, and are able to identify Frank as the perpetrator based on his shoes, which are caught on tape.
Meanwhile, Frank chases Debbie through the house, during which she disfigures him by burning his face. He continues to pursue her, attempting to impale her with a processional cross. Debbie manages to stop him by shooting at him with a nail gun. Abigail returns and finds Frank, apparently dead, but he reawakens and begins strangling her. Using the processional cross, Debbie stabs Frank through the chest, impaling him to death. Later, Debbie and Abigail are escorted out of the house by police. A detective shows Debbie a photograph of an infant boy—the priest's illegitimate son—found at the crime scene. He asks if it is hers, to which she responds that it belongs to the house.
