Plot

Newlyweds are terrorized by demonic forces after moving into a large house that was the site of a grisly mass murder a year before.

December 1975. George and Kathy Lutz of Deer Park, New York recently married, this marriage her second following the death of her first husband. In part to begin a new life with her three children - Billy, Michael and Chelsea - especially as George tries to eke out his place in their life which is not to replace the memory of their father, George and Kathy want to buy another house in which they will live, they with a financial hurdle as George builds his contracting business. In nearby Amityville, they find what they consider the perfect waterfront colonial which they are surprised is just within their price range. After falling in love with the house, they learn that the reason for the low asking price is that one year previous, the former owners, the DeFeos, were murdered in the house. With this information in hand, they proceed to buy the house anyway, with George planning to turn the basement into an office for his business. Before buying the house, they are unaware of the details of the mass murder, where 23-year-old Ronald DeFeo Jr. had moved back in with his family, he living in the basement. He progressively began to feel possessed when finally on his 28th day in the house, he killed his parents and four siblings in the middle of the night, hearing voices telling him to kill them. After the Lutzs move into the house, some of the family members begin to see visions and have hallucinations, none of them telling the others for one reason or another. Slowly, the forces within the house begin to consume them to various degrees where they know that something is not quite right. The questions become if they will figure out that there is a force overtaking them before they are no longer able to get away, or if they are doomed to the same fate as the DeFeos on the 28th day of their residence. If the latter be the case, there will be the next Ronald DeFeo Jr. who will be the one of who the rest of the family needs to be wary.—Huggo

In December 1975, George and Kathy Lutz along with their three children are moving into an elegant house in Amityville, Long Island. What they don't know is that six gruesome murders were committed there the year before - Ronald DeFeo Jr., the oldest son in the family, murdered his parents, his two brothers and two sisters by shooting them with a .35 caliber in November 1974. No sooner are the Lutzs moved into the house than they begin seeing horrible things - the ghost of Jodie DeFeo, horribly disfigured bodies - and hearing ghostly voices through the house. George seems to notice it the most, and it isn't long before he becomes a danger to those around him. When the local priest called into bless the house, comes charging out in horror after being swarmed by flies, he issues a dire warning to Kathy - "Leave that house". But will they be able to escape before the house and its vengeful spirits take control of George - and make him into a deadly menace?—Derek O'Cain

On November 14, 1974, the police received a frantic phone call that lead them to the house at 112 Ocean Avenue, where they made a grisly discovery - six bodies, the entire DeFeo family, all murdered with a .35 caliber as they sleep calmly in their beds. Ronald DeFeo Jr. confessed to methodically murdering his parents and four siblings, and claimed it was the voices that ordered him to do it. One year later, on December 18, 1975, the newly married couple George and Kathy Lutz along with their three children moved into the house, thinking it was going to be their dream house. They decide to keep the house and attempt to keep the horror in the past, especially if their dreams were nightmares. The Lutz family only lasted 28 days in their house after they were terrorized by demonic forces that drove them away. Based on the true story of George and Kathy Lutz, The Amityville Horror remains one of the most horrifying haunted house stories ever told - because it actually happened.—Scott

At 3:15 am on November 13, 1974, the entire DeFeo family was murdered at their house at 412 Ocean Avenue in Amityville, Long Island, New York. The oldest son, Ronald DeFeo Jr. confesses to the police that he heard voices in the house, and he was persuaded to kill all six family members. One year later, a married couple, George (Ryan Reynolds) and Kathy Lutz (Melissa George) move into the house with Kathy's three children from a previous marriage, Billy, Michael and Chelsea. Unfortunately, their dream house becomes a nightmare as the family soon begins experiencing paranormal events in the house. Chelsea (Chloe Grace Moretz) claims that she has made friends with a young girl named Jodie, a name belonging to one of the murdered DeFeo children.

One night, the married couple decided to leave and hire a babysitter to watch the three children. When the babysitter, Lisa (Rachel Nichols), arrives, they learn that she has been previously hired to babysit for the DeFeos. Lisa tells them about the murders that took place in their house. When she goes to Chelsea's room, Chelsea tells her she is a bad babysitter, claiming Jodie told her so. Lisa begins to scold Jodie for being the reason behind her getting fired. Then Billy dares Lisa to go inside the closet (the same closet where Jodie was murdered), and she gets locked inside. After a few seconds, she encounters Jodie and begs to be released. She goes into shock and the paramedics arrive to take her away; on the way to the hospital, Lisa tells Kathy that she has seen Jodie.

Unfortunately, George's behavior towards Kathy and her children becomes abusive and the paranormal activity continues. One night, George hears Harry barking in the boathouse. Seemingly possessed, he grabs the axe and proceeds to murder the family dog after mistaking this for a demonic apparition. The children look for Harry the next day, with George denying he knows where he is, despite Billy's suspicions.

Kathy asks the priest Father Calloway (Kevin Peter Hall) to bless the house, as a protective measure to prevent any future paranormal occurrences, but Father Calloway flees the house when he encounters such occurrences himself. Kathy discovers that the house once belonged to a cult preacher named Reverend Jeremiah Ketcham, whose evil actions towards Native Americans during his mission in 17th century Amityville are said to be the cause of the haunting. Meanwhile, as George is walking through the basement of the house, he encounters the apparitions of the Native Americans who were tortured and killed there by Ketcham centuries ago. Entering a dimly lighted room, George encounters Ketcham himself (though he is unaware of who he is), and the ghostly figure of the evil missionary turns around, picks up a knife, and slits his throat in an action of recreating his suicide, covering George with blood, and causing him to become nearly completely possessed.

Kathy becomes convinced that George's abusive behavior is owed to a spiritual possession. Following urgent advice from Father Calloway, Kathy attempts to evacuate her children from the house and escort them to safely, but the possessed George attempts to kill her and the children; Kathy knocks him out to prevent him from doing so and transports him away from the residence via motorboat. Subsequently, George is released from the spirit's possession and the family permanently leaves the house. A title card states that the family departed within 28 days of arriving and never returned. Jodie is shown standing in the now-empty house and screaming in terror while the house rearranges itself back to its original state before the family's arrival. Subsequently, she is pulled beneath the floor by a pair of disembodied hands.