Tess Marshall arrives at a rental house in the rundown Detroit neighborhood of Brightmoor on the evening before a job interview. However, she finds it has been double-booked and is already occupied by a man named Keith Toshko. Initially unnerved by Keith, Tess warms up to him and decides to stay the night while Keith sleeps on the sofa. When she wakes up in the middle of the night, she is shaken to find her bedroom door has been opened, but Keith is asleep and assures her he did not touch the door.Tess goes for her interview the next morning and is cautioned to stay on guard while in the neighbourhood around the house, which is suffering from heavy urban decay. Returning to the house, she is chased inside by a homeless man who yells at her to leave. She accidentally locks herself in the basement and stumbles across a hidden corridor, leading to a room with a camcorder, a stained mattress, a bucket, and a bloody handprint.Keith returns to the house, frees Tess from the basement, and investigates the hidden corridor. When he does not return, Tess follows him and finds a subterranean tunnel attached to the hidden corridor, where she finds Keith injured. While they argue about where to go, the pair are attacked by a naked, deformed woman (credited as "The Mother") who kills Keith by violently bashing his skull against a wall.Two weeks later, the house's owner, actor AJ Gilbride, is fired from a television series over allegations that he raped his co-star (something that is confirmed in a conversation with his friend later). Pressured to sell assets to pay his legal costs, AJ travels to Detroit to inspect the house before selling it. AJ finds the hidden tunnel and tries to measure it, believing it may increase the house's value. The Mother attacks AJ in the tunnel and he falls into a hole where he meets Tess.A flashback to the 1980s shows Frank, the house's original owner, abducting women, raping them, and keeping them captive in the tunnels, where it is implied that he rapes the offspring.In the present, the Mother locks Tess and AJ in a hole. Tess tells AJ that the Mother wants them to act as her children. AJ is dragged away by the Mother, who forcibly breastfeeds him. Tess uses the opportunity to escape the house with the help of Andre, the homeless man from earlier, who warns her that the Mother will come after her at nightfall.With the Mother distracted by Tess's escape, AJ finds a room which the Mother refuses to approach. Inside, he finds a bedridden Frank and assumes him to be another victim of the Mother. AJ assures Frank that he will call the police, before finding evidence of Frank's crimes. Frank kills himself with a concealed revolver.Tess leads police to the house, but they dismiss her story and leave as night falls. Tess breaks into the house, retrieves her car keys, and rams the Mother with her car, seemingly killing her. Tess returns to the basement to rescue AJ. AJ, assuming her approaching footsteps are The Mother's, mistakenly shoots her with Frank's gun. The two escape and find that the Mother has vanished. Tess and AJ then take shelter with Andre.Andre explains that the Mother is a product of Frank's multi-generational incest with his victims. The Mother bursts in, kills Andre by ripping his arm off and beating him to death with it and chases Tess and AJ up a water tower. AJ loses his gun and pushes Tess off the water tower to save himself. The Mother jumps after her and shields her from the fall. AJ finds Tess is still alive, but as he tries to rationalize his actions to Tess, the Mother revives and gouges his eyes out, killing him. The Mother attempts to comfort Tess, but she remorsefully shoots the Mother dead with Frank's gun and limps away as the sun rises.