The movie begins on a rainy night. We see the infamous Amityville Horror house. Six priests, led by Father Manfred (Norman Lloyd) enter the house and start to exorcise it. One of the priests, Father Dennis Kibbler (Fredric Lehne) is in an upstairs bedroom and begins to bless it when he sees a glowing brass floor lamp. As he begins to chant, a burst of energy emerges from the outlet, through the cord, and into the lamp. A demonic face appears in the large round bulb. Kibbler is knocked across the room and is unconscious.
A few days later, the real estate agency decides to have a yard sale by selling the items left in the house by the previous owners. Father Manfred believes that the evil spirits are finally gone from the house. Meanwhile, at the yard sale, a woman named Helen Royce (Peggy McCay) and her friend Rhona (Gloria Cromwell) are looking through the items when Helen finds the lamp. At only $100.00, Helen decides to buy the lamp. She even decides to send it to her sister as a birthday present, explaining that she and her sister send each other rather ugly gifts as a long-running joke. While checking the lamp, Helen cuts her finger on a brass collar around the bulb. Ignoring the cut on her finger, Helen buys the lamp. As the day goes on, Helen's finger begins to get infected and discolored. Helen later dies of Tetanus.
One week later, the lamp arrives at Helen's sister, Alice Leacock's (Jane Wyatt), house, a large, three story home over a beach in a small town called Dancott, California. That day, Alice's daughter, Nancy Evans (Patty Duke) and her three children Amanda (Zoe Trilling), Brian (Aron Eisenberg), and the youngest child, quiet, mysterious Jessica (Brandy Gold) move in with Alice. Once they arrive, Alice decides to open the package containing the lamp. Nancy thinks the lamp is hideous, while Alice finds it to be interesting. Once the lamp is turned on, Alice's parrot, Fred, begins to act crazy, and her cat, Pepper, scratches Amanda. While the rest of the family pays little to no attention to the lamp, Jessica seems to be drawn towards it.
The lamp then begins to manipulate electrical devices around the house or perform seemingly impossible feats, such as killing the parrot and putting it in the toaster oven, turning on the kitchen sink's garbage disposal and cutting off the hand of Amanda's boyfriend, and vandalizing Jessica's room.
When Nancy calls a plumber to fix the pipes, the lamp murders him by drowning him in tar, and then makes his car leave on its own, making it seem like he left. Jessica is drawn to the lamp and starts to believe her dead father's spirit is inside it. Meanwhile, Father Kibbler, while staying at Father Manfred's place, gets a call from the lamp which makes smoke come out of the phone and melts the speaker. Worried, he travels to Dancott to investigate. When most of the family is away, Jessica is entranced by the lamp, which then uses its extension cord to murder their housekeeper Peggy.
The police investigate though they do not find the plumber's body. Father Kibbler contacts Nancy and tries to convince her that the evil has taken possession of an object from the Amityville house. They rush home only to find that the lamp used a window to knock out Amanada and has brainwashed Jessica, who stabs Father Kibbler in the shoulder, while the lamp's extension cord tries to stop him from exorcising it. The day is saved by Alice who grabs the lamp and throws it out of the window, shattering it on the rocky shore. The movie ends with the family thinking their ordeal is over, not realizing that the dead plumber is still inside their house. The camera pans to the remains of the lamp, showing the evil within has now possessed the family's cat.Patty Duke as Nancy Evans
Jane Wyatt as Alice Leacock
Fredric Lehne as Father Kibbler
Lou Hancock as Peggy
Brandy Gold as Jessica Evans
Zoe Trilling as Amanda Evans (as Geri Betzler)
Aron Eisenberg as Brian Evans
Norman Lloyd as Father Manfred
Robert Alan Browne as Donald McTear
Gloria Cromwell as Rhona
James Stern as Danny Read
Peggy McCay as Helen Royce
Despite the destruction of the house in the conclusion of the previous film it manages to make an appearance in this film. The films after 3-D usually do not pick up where the previous film left off, so no explanation has ever been given as to how the house is still standing. It is possible this film may take place before Amityville 3-D due to the house already being empty in that film, and after the yard sale in this one. The furniture that was left in the house in the beginning of the film is believed to be owned by the Lutz family in the first movie. The film also makes a reference to Amityville II: The Possession.
On The A.V. Club web site, Amityville 4 is one movie listed in the article "Night of the Killer Lamp: 23 Ridiculous Horror-Movie Adversaries". The article states the film's efforts to make a possessed lamp seem scary "border on camp".
The replica of the original Amityville house was located at 402 East M St., Wilmington, California. A facade was added to the side of the house to give it the Amityville appearance. The interiors of this house were filmed also.
The exteriors for Alice Leacock's house were filmed at the James Sharp House, 11840 W. Telegraph Rd, Santa Paula, California. The house is an historical Italian Villa style home built in 1890. In reality, it does not back out onto an oceanside cliff as depicted in the movie. Instead, it backs out onto the Santa Paula Freeway, about a quarter of a mile behind the house. For a second, you can see the tower of the house in the distance while driving on the Freeway.
The interiors of the grandmother's house were filmed at the Woodbury-Story House in Altadena, California.
An exterior shot of the John Marshall High School in Los Angeles, California was also used.