On Christmas night, the story begins with a tense and eerie scene as a bathtub overflows, causing water to flood the house. The camera traces the water as it makes its way downstairs to the main floor, revealing Edna ([Robyn Nevin](../actor/robyn-nevin))—an elderly woman who appears to be in a trance. In a corner of the room, an ominous figure stirs within the shadows, hinting at something sinister lurking within the house.
Fast forward a year, Edna’s daughter, Kay ([Emily Mortimer](../actor/emily-mortimer)), and her granddaughter, Sam ([Bella Heathcote](../actor/bella-heathcote)), arrive at Edna's crumbling home, concerned because Edna hasn't been seen or heard from recently. Their arrival is marked by strange noises, creaking floors, and a house that seems to be deteriorating before their eyes. They notice many doors have been locked anew, clutter piles up, and mold spreads across walls and furniture. Edna has also left cryptic post-it notes throughout the house—some mundane, like “set the alarm,” but others disturbing, such as “do not follow it,” which suggest her mental state might be declining rapidly.
The family contacts the police, initiating a multi-day search. During this time, Sam experiences unsettling phenomena, such as a mysterious breathing sound in a closet that she cannot explain. Additionally, Edna’s neighbor's son, who has Down syndrome, refuses to come inside the house, adding an unsettling layer to the house's dark mood.
One night, Kay dreams of visiting an old cabin deep in the woods where she finds her mother sitting quietly. As she enters, an old, decayed man appears, covered in filth and neglect, with black mold beginning to crawl over the windows, symbolizing corruption and decay. The next morning, Edna is found in the kitchen making tea, but she doesn’t disclose where she's been, nor does she seem entirely herself. A doctor examines her and notices a large black mark on her chest but reports that physically, she seems healthy. The family debates whether to place Edna in a nursing home, while Edna gives Sam a family heirloom ring, emphasizing her connection to the family.
Sam, meanwhile, uncovers a sketchbook belonging to Kay’s father, revealing a drawing of the cabin from Kay's dream. Kay shares that this cabin was the first house on the property and was home to her great-grandfather, who eventually died—ostensibly from dementia—abandoned by his family. Portions of that old house were incorporated into Edna’s current home, blending history and unsettling mysteries.
That night, Kay hears her mother talking to herself and notices Edna asking her to check underneath the bed, where she previously saw something breathing. Edna’s increasing forgetfulness and paranoia become more evident as she claims "something" entered through the closet, and she increasingly perceives the house as unfamiliar—loss of memories very much intertwined with her surroundings. Disturbingly, Sam is frightened when her washing machine randomly turns on and off, heightening the sense of a malevolent presence.
The following morning, Sam discovers Edna speaking to herself and cutting her hand with a knife. When she intervenes, Edna’s behavior turns violent, attacking Sam over a ring that Edna claims to be hers. The neighbor then recounts a chilling story: Edna had played hide-and-seek with his son, locking him in the closet for hours, causing screaming and distress, and since then, the child had been barred from coming inside, hinting at past abuse or darker secrets.
In a poignant moment, Kay follows Edna into the woods, where she finds her mother attempting to eat photographs and bury photo albums. Edna confesses she believes these are the only ways to protect the memories from something dark she senses within the house. Kay, overwhelmed with emotion, pleads with her mom to move in with her rather than face continued deterioration.
Soon after, Sam explores the walk-in closet and finds a hidden passage leading into an entire labyrinth within the house—an ever-changing maze that seems to distort reality. She tries to retreat but finds herself lost, with the house growing increasingly surreal and hostile. Post-it notes with Edna’s handwriting hint that this labyrinth may be where Edna herself has been lost.
Kay and Edna return home, desperately searching for Sam, but she is nowhere to be found. As Kay prepares a bath, she notices the black mark on Edna’s chest expanding, and she finds Edna locked outside the bathroom. Through the window, she witnesses Edna stabbing herself in the chest, leading Kay to break down the door. Edna runs into the labyrinth, and Kay chases her into the maze's dark, twisting corridors.
In a harrowing scene, Edna peels off her human skin, revealing a horrifying, demon-like black dermis underneath, confirming that her apparent dementia and strange behaviors are actually the result of a possession. It’s implied that this same affliction plagued her great-grandfather, connecting generational trauma.
Fleeing from the demonic Edna, Kay finds Sam inside the labyrinth. Together, they attempt to escape by smashing through the labyrinth wall into the house and climbing out. The demonic Edna attacks, and a desperate fight ensues, with Kay wielding a steel pipe to fend her off. Eventually, Kay fatally wounds the demonized Edna, and both Kay and Sam begin to run away from the collapsing house.
As they escape, Kay hears the haunting whisper of her mother, and she recalls the story of how her great-grandfather was abandoned and lost in a similar maze. Before leaving, Kay carefully places the disfigured, skinless Edna back onto the bed, kissing and tucking in what is left of her, signifying her acceptance of the dark truth.
Sam joins her, and both women crawl into bed—an act symbolizing a fragile sense of peace but hinting at the continuing presence of evil. As the scene closes, Sam notices a small black mark on Kay’s back, suggesting she might be destined to suffer the same fate as her mother and grandmother. The film ends with a chilling view of the cabin window from Kay's dream, now engulfed in black mold, leaving the audience with a haunting impression of the dark and inescapable cycle that has haunted multiple generations.
