Writer Ben Rolf, along with his wife Marian and their 12-year-old son Davey, embarks on a summer escapade to a large, shabby, neo-classical mansion that has seen better days. Owned by the eccentric elderly siblings, Arnold and Rosalyn Allardyce, the mansion is offered to them at a seemingly unbeatable price of $900 for the entire summer. However, there is a peculiar stipulation: the Allardyces' elderly mother will remain in her upstairs suite, and the Rolfs are required to deliver her meals throughout their stay. An odd character with an overwhelming need for privacy, she prefers to remain hidden, leaving her meals untouched in her sitting room outside her locked bedroom.
Upon their arrival, they are joined by Ben's elderly Aunt Elizabeth. Fascinated with their new surroundings, Marian becomes increasingly absorbed in the home's care, even donning the Victorian-era garments she discovers in Mrs. Allardyce's suite, while creating emotional distance from her family. Of special interest to her are the many portraits adorning Mrs. Allardyce's sitting room, which depict various former inhabitants of the mansion. Intriguingly, Marian notes that Mrs. Allardyce's meals remain mostly untouched, a curious detail that contributes to the unsettling atmosphere they've encountered.
As summer unfolds, peculiar events occur—after Davey suffers an injury while playing, a once-dead plant begins to flourish again, Ben cuts his hand on a champagne bottle only to find a light bulb mysteriously restored, and Ben is haunted by the chilling vision of a malevolent hearse driver he recognized from a past funeral. Each incident seems to breathe new life into the house, suggesting that it draws energy from the family, revitalizing itself as their misfortunes unfold.
As the days pass, Marian's demeanor shifts; she becomes increasingly possessed by the house's peculiar energy. When Aunt Elizabeth suddenly falls ill and passes away, the dead flowers in the solarium spectacularly come back to life. Despite the tragedy, Marian's fixation on the home remains unwavering, leading to a confrontation with Ben who is enraged by her indifference to the funeral. Determined to leave, he discovers that the house is not just a structure but appears to be a living entity as he witnesses the old shingles and siding falling away, replaced by fresh ones.
In a desperate attempt to escape with Davey, Ben finds the road blocked by a tree, only to catch sight of Marian transformed into the chauffeur. Overcome with despair, he becomes catatonic. The next day, as Davey enjoys a swim while a comatose Ben keeps watch, the serene pool tragically turns into tumultuous waves, threatening to engulf the boy. Marian jumps to save her son, which brings Ben back from his stupor. Although Marian believes it's time to evacuate, she insists on checking on Mrs. Allardyce first. When she doesn't return, Ben begins to search for her, only to be horrified when he realizes that the elderly woman upstairs is, in fact, his wife, who has inexplicably aged.
"I've been waiting for you, Ben!" she proclaims, leaving him in shock. Meanwhile, Davey, awaiting in the car, witnesses his father plummet from the attic window, landing on the windshield in a disturbing fashion. Traumatized, he rushes toward the house, only to face a tragic fate when a chimney collapses on him.
In the aftermath of these harrowing events, the Allardyces revel in the magnificence of their revitalized home while celebrating the return of their "mother." In Mrs. Allardyce's sitting room, the portrait collection now eerily features images of Ben, Davey, and Aunt Elizabeth, signifying the house's insatiable connection to its inhabitants.
