The story concerns a young woman named Julia (Lee Purcell) who goes to live with her aunt's family after she loses both her parents and their housekeeper in a car crash. Although they haven't seen her in ten years, Julia's aunt Leslie, her husband Tom (Jeremy Slate), her son Peter (Jeff East), daughter Rachel (Linda Blair) and youngest son Bobby (James Jarnigan) are all eager to make the new member of the house feel welcome. Rachel is especially thrilled at the thought of having a girl her age around the house and even offers to split her bedroom with her cousin, but Julia seems painfully shy. The family takes note of her strange accent, as it's not the way most people who live on the east coast speak. Trying to open up a bit, Julia gets a makeover and develops a more sophisticated façade.
One day, Rachel's horse Sundance attacks Julia and tries to trample her. Julia recovers and begins insinuating herself into the family. Rachel's brother and dad seem particularly taken with the fetching young lady in their midst. Odd things begin to happen. After having earlier found a human tooth among Julia's belongings, Rachel discovers a photo of herself missing...and her face breaks out in blotchy hives. She also begins to notice that Julia doesn't always have a reflection in the mirror. The hives render Rachel unable to attend a dance. Julia accompanies Rachel's boyfriend Mike (Jeff McCracken) instead, borrowing a dress that Rachel had made for herself; an arrangement that Rachel should never have agreed to because Mike becomes smitten with Julia and they begin dating. To make matters worse, the cousin also forges a close friendship with Carolyn (Fran Drescher), Rachel's best friend. The next day, Rachel enters into a competition with Sundance, where the horse flips out, breaking its leg in the process and forcing a vet to put it to sleep.
To her surprise, Rachel finds things in Julia dresser drawers that point to something sinister - burned hair from her fallen horse and her missing photo covered in red paint spots. She speaks to Professor Jarvis (Macdonald Carey) who tells her it may indeed be the work of someone who practices black magic. Before she can show him the evidence however, the professor collapses and is rushed to the hospital. A letter that Julia receives from a friend gets the best of Rachel's curiosity. Rachel phones the friend in Boston and discovers that Julia supposedly sings in her school's glee club. Knowing that the person living in her house doesn't have any interest in music, Rachel further suspects something is not right. Immersing herself in books on the occult, Rachel starts to believe Julia is a witch. During a visit to the professor at the hospital, he tells her that witches do not show up in photographs. A camera is a machine and machines cannot be coerced, she's told. The next day, Rachel encourages her mother to take pictures of the reluctant cousin. Everything comes to a head when Leslie plans a road trip and Rachel finds a map with burn marks on it. It looks as if Julia is planning on causing her mother to have an accident. She also sees Julia overtly seducing her father.
Too late to stop Leslie from leaving on the trip, Rachel develops the roll of film herself and clearly sees that her suspicions have been correct all along...Julia is nowhere to be found in the photos. Suddenly, Julia comes pounding into the darkroom and the two have a fierce struggle. Rachel manages to break away and she locks the door to the room. She then evades her dad, who tries to stop her. Julia breaks out of the room...her eyes a ghastly white and red. Rachel rushes over to Mike and tells him to get in his car so they can find her mother. Julia takes off after them, hitting Mike's car and trying to drive them off the road. Finally, Rachel and Mike catch sight of Rachel's mom, whose car causes Julia to drive off a cliff to a fiery explosion below. It is then revealed that the real Julia perished alongside her parents in the car crash, and that it was actually Sarah, their housekeeper, who survived the accident. The Bryant family tries to return to normal. Meanwhile, another family welcomes a new nanny into their household. A woman who looks remarkably like the stranger who terrorized the Bryant home...Linda Blair as Rachel Bryant
Lee Purcell as Julia Grant / Sarah
Jeremy Slate as Tom Bryant
Jeff McCracken as Mike Gallagher
Jeff East as Peter Bryant
Carol Lawrence as Leslie Bryant
Macdonald Carey as Professor Jarvis
James Jarnigan as Bobby Bryant
Fran Drescher as Carolyn Baker
Kerry Arquette as Anne
Sierra Pecheur as Nurse Duncan
Billy Beck as Sheriff
Patricia Wilson as Mrs. Gallagher
Frederick Rule as Mailman
Helena Mäkelä as Beverly Hills Lady
The film marked starlet Linda Blair's third leading role in a horror film, following her Oscar-nominated performance in The Exorcist and its sequel Exorcist II: The Heretic. In his DVD commentary, director Wes Craven recalled that Blair had recently "gotten into some trouble" prior to filming; also that he was plainly inspired by Roman Polanski's work, and tried to carefully build a sense of paranoia and suspense in the film's narrative.
The home used in the movie is located at 5950 Spring Valley Road, Hidden Hills, California. The house was owned by comic actor Sinbad from 1997 until 2010, when he was forced to sell for his debts for the price of $1.8 million to Rugby Hall of Famer Shawn Lipman.
Stranger in Our House first aired on television on NBC-TV on October 31, 1978.
The film was released in the United States on DVD on February 18, 2003 through Artisan Entertainment. On June 1, 2017, it was announced that the film would be receiving a Blu-ray and special edition DVD release through Doppelgänger Releasing.
From contemporary reviews, the Monthly Film Bulletin "takes a long time to convince that something really devlish is lurking in California's green and pleasant pastures" The review noted that Ms. Purcell "deserves to survive this farrago rather more than the satanic Beverly hillbilly she plays."
AllMovie called the film "a modestly entertaining horror item." While the film hasn't garnered enough reviews to receive a rating on movie review aggregator website Rotten Tomatoes, all four listed reviews are negative.