Backrooms

In June 1990, a researcher with the Async Research Institute, Naren Warne, is separated from his group and becomes lost in "the Backrooms", a labyrinthine extradimensional space containing a chaotic expanse of dull yellow rooms, fluorescent lights, long corridors, and malformed furniture. While attempting to call for rescue, Naren is chased and attacked by an unseen entity. Async scientists watch the recovered footage of the incident.

Clark, a failed architect who owns a struggling furniture store, attempts to cope with his alcoholism and crumbling marriage. He sees therapist Mary Kline, who is working through trauma from demolition of her childhood home and her agoraphobic mother's institutionalization. Clark recruits his assistant manager Kat and her boyfriend Bobby to film a television commercial featuring himself dressed as the store’s pirate mascot. Having taken up residence in the store, he notices the lights flickering mysteriously at night and his television functioning erratically. While checking the breaker box, Clark notices a glowing slit in a wall. Approaching it, he falls through and enters the Backrooms. Clark finds Naren's belongings and narrowly escapes back to the store when an unseen entity chases him. An Async scientist, Phil, watches these events on a surveillance camera.

Clark tells Mary about the Backrooms but is met with skepticism. In need of proof, Clark brings Kat and Bobby into the Backrooms to film their discoveries. Bobby explores a steeply sloped corridor and is ambushed and dragged away by an unseen entity; Clark and Kat frantically give chase and are drawn into an unexplored area where they are separated. Clark runs through various bizarre and disordered spaces, eventually encountering two other humanoid entities that chase him to a dead end. He hears Kat call out to him and sets the camera down to look for her. Something picks up the camera as Kat screams for Clark to look behind him.

Some time later, Mary receives a cryptic answering machine message from Clark, who tells her that he is staying in the Backrooms and will not return. Phil watches television with his family and recognizes Clark in a commercial for the furniture store. Concerned about Clark, Mary visits the store and enters the Backrooms herself. An apparently psychotic Clark arrives; hearing an entity approaching, he tries to calm Mary before choking her unconscious.

Mary awakens tied to a chair in a space resembling a dining room occupied by Clark and three malformed, unmoving imitations of humans. They stare impassively as Clark stabs one of them, demonstrates they are made of an edible white substance, and reveals Kat's severed head in a refrigerator. Clark demands that Mary continue their therapy sessions, but she instead scolds Clark, telling him that his wife left him for his inability to take responsibility for his failures. He begins to release Mary, but is interrupted by the arrival of a towering, distorted simulacrum of Clark dressed as the store's pirate mascot. Clark tries to calm the pirate monster, which suddenly kills him and then chases Mary through various chaotic and surreal spaces to a flawed replica of the furniture store. Cornered by the monster, she bashes it in the face using a chunk of concrete from her childhood home. Their struggle triggers an Async gas trap, alerting a group of researchers in hazmat suits; the monster is subdued, and Mary is taken to their research facility.

After recovering, Mary is taken to an interrogation room where she meets Phil. He explains that Async made magnetic resonance imaging machines until they discovered the Backrooms, which have since become their primary research focus. When asked how she came across the Backrooms and what she found there, she repeats Clark's description of it as a faulty, misremembered copy of reality. Mary asks if Async will let her go, but Phil vaguely replies that the decision is not up to him. Inside the Backrooms, a series of spaces are limned by Mary's memories and trauma, ending in a loosely copied interrogation room in which a deformed simulacrum of Mary sits still and silent.