NOTE: This spoiler was submitted by Jeremy

The film opens on a stormy night. Tess Marshall (Georgina Campbell) arrives at an Airbnb that she booked at 467 Barbary Street, but as she tries to check in, she cannot find the house key or get in touch with whoever booked her. Before she leaves, she sees a light turn on in the house, and she rings the bell. A man named Keith Toshko (Bill Skarsgard) answers, and he says he booked the house as well. Since they cannot reach the bookers, Keith invites Tess to stay while they try to get things sorted.

Tess is unable to book a hotel anywhere else, so she takes a shower and is invited by Keith to share a bottle of wine. She explains that she is meeting with a filmmaker named Bonnie Zane (Sophie Sorensen) for a job interview. Keith says he has seen her last film, despite Tess thinking nobody else would have seen it. They bond for a bit before going to bed.

During the night, Tess wakes up to overhear Keith gasping in his sleep, likely due to night terrors. She tries to wake him up but ends up startling both of them. Keith denies anything is wrong.

The next day, Tess goes for her interview. As she steps outside, she is surprised to see that all the other houses surrounding the AirBnB seem abandoned and dilapidated. Tess then goes to meet Bonnie at the restaurant. Everything goes well until Tess mentions where she is staying, and Bonnie warns her to get out of there quickly.

When Tess returns to the house, a man named Andre (Jaymes Butler) runs after her and tells her to get out of the house. Although a bit spooked, Tess goes about her business and ends up going down toward the basement. The door locks behind her, and she has left her phone on the kitchen table. She then finds a rope attached to the wall and finds a secret entrance to a tunnel. Despite some initial hesitance, Tess goes into the tunnel for a little bit. She comes across a room with a bed, a camera, and a bloody handprint on the wall, as well as a staircase going further down, causing her to freak out. She runs back to the basement and sees Keith outside, so she gets him to help get her out.

Tess explains to Keith what she saw and says they need to get out of there. Keith tries to reassure her that there is nothing serious down there, so he goes to check it out. After a while, Tess goes looking for Keith, and she walks down the staircase. She hears Keith screaming and calling for help. Tess finds him in the tunnel, and he says something bit him. Before they can run, a horrifying naked humanoid monstrosity, “The Mother” (Matthew Patrick Davis), appears and smashes Keith’s head until he is dead before she roars at Tess.

An undisclosed amount of time later, screenwriter AJ Gilbride (Justin Long) is driving when he gets a call from his colleagues. They tell him he is being dropped from their latest project because a woman is alleging that AJ raped her. He maintains his innocence, but even his accountant drops him from representation. AJ later goes out with a friend, all but outright admitting that he pressured the woman into sex.

AJ later goes out of state to the house he is renting, which happens to also be the Barbary house. He arrives and finds Tess’s luggage before going into the basement to investigate. He is found and chased by The Mother before he falls into a pit where Tess is being kept as well.

Jump back to sometime in the 80’s, when Barbary Street was full of residents. A man named Frank (Richard Brake), who lives in the same house, goes to a store to get baby products. He then spots a young woman and follows her back to her house. Frank dresses as a man from the electric company to get inside her house and unlock her bathroom window. When he returns home, his neighbor Doug (Kurt Braunholer) tells Frank that he and his wife are selling their house.

Back in the present, Tess tells AJ to be quiet and calm down. The Mother then lowers a baby bottle down into the pit, which Tess drinks from, but AJ is less willing. The Mother enters the pit and treats Tess like her child, but she growls and screeches toward AJ. Tess and AJ manage to climb out of the pit and begin to make their way out, but AJ is left behind and trapped in a room where The Mother forces him to breastfeed off her. Tess manages to break the window to the basement and is pulled out by Andre before The Mother can reach her. Andre tries to take Tess to safety, but she insists on going back to free AJ.

Tess calls the cops, but when they arrive, they believe that she is a strung-out addict due to her disheveled appearance. She brings them to the house, but since she has no proof that there is any evidence of a crime, the cops leave.

Tess waits until it gets dark to break into the house and get her keys. When she gets into her car, The Mother emerges and tries to break into Tess’s car, but she drives into the side of the house to try and kill The Mother, but it just briefly knocks her out.

Meanwhile, AJ has made his way into a room where he finds Frank, bedridden and close to death. AJ sees several tapes that Frank has kept of the women he has raped over the years. As AJ calls him out for how sick he is, Frank pulls out a gun and shoots himself in the head. AJ grabs the gun and goes out of the room. Tess is down there and calls out to him, causing AJ to get startled and pull the trigger. Tess is shot in the abdomen, but AJ helps her get out of the house. When they get outside, Tess sees that The Mother is not where she originally was. She tells AJ she knows where they can run to.

Tess brings AJ down by the water where Andre told her to go for safety. He explains to them that Frank owned the house and was most likely the source that booked the victims. He would kidnap women and rape them, producing children that he would also rape, and The Mother is a product of incestuous rape that has been in the house for over 40 years. Although confident that she cannot find them, Andre is quickly proven wrong when The Mother emerges and rips his arm off, then beats him to death with it.

Tess and AJ run for safety and make their way up a water tower. AJ drops the gun just as The Mother starts catching up to them. AJ thinks he can redeem himself and save both of them…so he grabs Tess and throws her off the tower, knowing The Mother will instinctively go after her “baby.” AJ runs down and sees The Mother seemingly dead. Just as he tries to justify his actions to Tess, The Mother springs back up and gouges AJ’s eyes out with her thumbs before cracking his head in two. The Mother then crawls over to nurture Tess, who grabs the gun. She has a slight look of remorse on her face before she pulls the trigger. Tess then gets up and walks out of the area to get medical attention.

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Tess Marshall arrives at 467 Barbary Street to stay at an Airbnb, only to find it has been double booked with another man named Keith Toshko. Tess stays the night but quickly discovers a sinister presence lurking in the house since there is a hidden tunnel in the basement. Keith ends up down there and is killed by a humanoid monstrosity known as “The Mother”.

A screenwriter, AJ Gilbride, who is facing rape allegations, goes to the same house since he is already renting it. He ends up in a pit in the basement along with Tess, as The Mother treats her victims like her babies. While Tess plays along, AJ is less willing. Tess is able to escape, but she gets no help from the police, so she waits until it’s dark to go back into the house to help free AJ.

AJ discovers a man named Frank, who is The Mother’s father, bedridden and close to death. After seeing evidence of Frank’s crimes in videotapes, Frank shoots himself in the head. Tess finds AJ but he accidentally shoots her in the abdomen. They run from The Mother and find a homeless man, Andre, who earlier warned Tess about being in the house. He explains that The Mother is a product of incest since Frank kidnapped and raped women and then raped the children, which is why The Mother is what she is. She shows up and kills Andre before chasing Tess and AJ up a water tower.

AJ makes an attempt to save his own skin by throwing Tess off the tower, knowing The Mother will instinctively try to protect her. It doesn’t kill her, and The Mother splits AJ’s skull in two. Tess grabs the gun and has a look of sadness on her face before she kills The Mother, and then leaves to get help.