In town for a job interview, a young woman arrives at her Airbnb rental late at night only to find that the house has been mistakenly double-booked and a strange man is already staying therComing into town for a job interview, Tess Marshall books a remote house in the rundown Brightmoor neighborhood of Detroit. Upon arriving at the house, Tess finds out that the place has been double-booked and is already occupied by a young man named Keith Toshko. Initially unnerved by Keith, Tess warms up to him and decides to stay the night.

The next morning, Keith leaves for the day, and Tess goes to her interview. The woman interviewing her sternly warns her that she should not be staying in the area of the AirBnB. She returns to the house and is chased inside by a homeless man yelling that she must leave. She ventures into the basement and gets locked downstairs, and stumbles upon a hidden corridor.

There, Tess finds a room with a camcorder, a stained mattress, and a bloody handprint. Tess backtracks and tries to leave but is still locked in the basement. Keith arrives and frees her. Tess tells Keith what she has seen, and he goes into the basement to investigate. When he does not return, Tess returns downstairs and discovers that the hidden corridor she had initially found leads to a subterranean tunnel, where she hears Keith screaming for help. She enters the tunnel and finds an injured Keith. The pair are attacked by a naked deformed woman, who brutally kills Keith.

Sometime later, actor AJ Gilbride learns he has been fired from his television series due to rape allegations made by a co-star. Pressured to sell his assets to pay for legal costs, AJ travels to a rental property he owns in Detroit, the same house that Tess and Keith rented. AJ inspects the house and eventually discovers the hidden tunnel. The deformed woman attacks him and he falls into a pit alongside Tess.

A flashback to the 1980s shows the house's original owner, Frank, who abducted women and held them captive in the tunnel. He would use the hidden room to videotape himself raping them, then rape the subsequent children.

In the present, Tess explains that the woman (referred to as "the Mother") wants them to act as her children. When AJ refuses to drink milk from a bottle offered by the Mother, she drags him away and forces him to breastfeed. Tess escapes and the Mother pursues her, allowing AJ to make his own escape. He discovers a decrepit Frank living further in the tunnel. Initially believing Frank to be another victim of the Mother, AJ assures Frank that the police will come to investigate. While AJ discovers the tapes, Frank discreetly retrieves a hidden revolver and kills himself.

AJ flees with the gun while the Mother leaves the house to find Tess. Tess escapes the house by breaking a basement window. She eventually reaches a gas station and is able to call the police. The officers are dismissive of her story, but she convinces them to go back to the house with her. The police refuse to investigate the house before being called away, attributing Tess' story and behavior to drug use.

After breaking into the house to retrieve her keys, Tess runs her car into the Mother, seemingly killing her. She returns to the basement to rescue AJ, but he accidentally shoots her. The two escape the house and find shelter with Andre, the homeless man who had chased her earlier.

Andre explains that the Mother is a product of multigenerational incest by Frank. The Mother ambushes the group