In Amityville, New York, John Baxter, a writer for Reveal Magazine, and his photographer, Melanie, attend a séance at a house that was once the site of a brutal multiple murder. Posing as a couple in mourning for their deceased son, John and Melanie expose psychics Harold and Emma Caswell as frauds, with Dr. Elliot West of the Institute for Psychic Research and David Cohler of the District Attorney’s office as their witnesses. The reporters return the following day, and are joined by Clifford Sanders, the real estate agent who owns the house. As they examine the Caswells’ special effects devices in the basement, Sanders falls through the floor into a dry well, and must be pulled to safety by John and Melanie. Later, Sanders assures John that he was unaware of the Caswells’ illegal activities, but adds that he was desperate for the rental income, as he has been unable to find a buyer. John dismisses the rumors surrounding the house and offers to buy it. Later, at the home of his estranged wife, Nancy, John removes the last of his possessions. He is joined by his daughter, Susan, and her friend, Lisa, both of whom are intrigued by John’s new home. Meanwhile, Melanie develops photographs in her darkroom, and notices two images of Sanders in which the agent’s face seems to be covered with flies. In Amityville, Sanders enters the house, then calls for John as he follows the sound of footsteps into the attic, where he is attacked by a swarm of flies. By the time John arrives, Sanders is in the throes of death. Melanie reaches the house as paramedics remove the body, and shows John the photographs, but he explains the anomaly as a probable defect in the film. She then brings the pictures to the Psychic Research Institute, where Elliot promises a full investigation, although he doubts that anything is amiss. At the Reveal offices, John leaves work early to meet with a literary agent, and invites Melanie to join him at his home for dinner that evening. On his way to the meeting, John is pestered by a fly as he enters an elevator, which suddenly stops between floors, speeds toward the roof, then drops to the bottom floor. He emerges shaken, but unharmed. Melanie arrives at the house ahead of John, as Dolores, the housekeeper, is leaving for the day. When Melanie is alone in the house, the temperature drops dramatically, and a frigid wind bursts from the basement, pinning her to the opposite wall. John returns home to find Melanie in a state of hysteria, and she swears to never return. Susan and Lisa explore the house in John’s absence, recounting the murders committed there years earlier. They move to the basement, where Lisa recalls a rumor that the property was once a Native America burial ground, infested with the ghosts of the interred. When Susan returns home, Nancy forbids her daughter from visiting the Amityville house, convinced something evil haunts the place. That night, when Melanie discovers a demonic face in photographs of the well, she places them in a file folder and drives toward the Institute for Psychic Research. A fly buzzes around her head as the brakes cease to function, and she crashes her car into a parked truck. The folder bursts into flames, which spread through the car, reducing Melanie to a charred skeleton. Days later, Susan defies her mother and brings her friends, Lisa, Jeff, and Roger, to the house, where they hold a séance in the attic, using a makeshift Ouija board. Ignoring the board’s warning that Susan is in great danger, they go for a ride in a motorboat docked nearby. When Nancy is unable to locate her daughter, she drives to Amityville. Once inside the house, she encounters Susan’s ghost, soaking wet and silently ascending the stairs to the attic. Outside, paramedics struggle in vain to revive Susan after she is pulled from the water. John arrives moments later and tries to convince Nancy that their daughter is dead, but she refuses to believe it and waits for Susan in the attic. The next morning, John awakens to find the kitchen in shambles while Nancy calmly irons Susan’s clothes, explaining that their daughter caused the damage in order to prove she is still alive. Concerned for Nancy’s sanity, John consults with Elliot, who offers to perform a complete scientific investigation of the house, to determine the presence or absence of supernatural activity. Elliot and his team place cameras and other monitoring devices around the property as Nancy remains seated in the attic. Suddenly, a purple apparition appears, and Susan’s voice is heard beckoning her mother to join her in the afterlife. Nancy follows the apparition into the basement, followed by John and Elliot, who prevent her from approaching the well, now filled with churning water. Elliot believes that the force from the well killed Susan, and intends to confront it. A demon rises from the water, breathes fire into Elliot’s face and pulls him into the well. With his final breath, Elliot tells Susan to save herself, and the apparition fades away. As the well bursts into flame and explodes, an icy wind blows through the house, tearing it apart from the inside out. John, Nancy, and only a few members of Elliot’s team escape before the house explodes. In the middle of the smoldering wreckage, a glowing purple fly buzzes around the well, spreading flames over the surface of the water.