The film immerses viewers in a chaotic night as Tess Marshall arrives at her Airbnb destination, 467 Barbary Street, only to encounter an aggravating dilemma – no key to enter and no means of contacting her booking party. As doubts set in, she notices a flicker inside the house and decides to ring the doorbell. To her surprise, Keith Toshko, another guest played by Bill Skarsgard, opens the door, claiming he too has reserved the same Airbnb. With no alternative options available, Keith extends an invitation for Tess to stay with him until they can clarify their reservations.
Tess, unable to find nearby accommodations, reluctantly accepts Keith's offer and freshens up with a shower. He offers her a glass of wine, and during their conversation, she reveals that she's in town for a job interview with filmmaker Bonnie Zane played by Sophie Sorensen. To Tess's astonishment, Keith admits he has seen her previous film despite its limited release. A connection blossoms between them as they retire for the night.
However, their peace is shattered when Tess awakens to Keith's labored breathing during the night. Her attempts to wake him lead to an alarming encounter, but Keith reassures her that everything is fine, dismissing her concerns.
The subsequent morning, Tess heads out for her interview but is struck by the eerie sight of forsaken and crumbling houses surrounding the Airbnb. At the restaurant, during her meeting with Bonnie, Tess casually mentions her accommodations, and Bonnie's demeanor shifts dramatically, urging her to leave that house at once.
Returning home, Tess is confronted by Andre, who frantically warns her to escape the house. His warning unsettles her, yet she continues her day, probing into the basement where she finds herself trapped as the door locks behind her. With her phone lying uselessly on the kitchen table, she discovers a rope secured to the wall leading to a hidden tunnel. Despite her trepidation, Tess dares to venture into the darkness.
This tunnel opens up to a chilling room equipped with a bed and a camera, marked distinctively by a bloody handprint smeared on the wall. Overcome with dread, she retreats but encounters Keith outside, who she desperately seeks help from. Despite being unsettled by her claims, Keith decides to delve deeper into the shadows for answers. Worrying for his safety, Tess follows after him, only to find him gravely injured and ranting about being bitten. Just as they contemplate their escape, an ominous figure known as “The Mother,” played by Matthew Patrick Davis, emerges and brutally crushes Keith’s skull, silencing him forever and directing a horrific roar at Tess.
Time becomes somewhat distorted as the story shifts, introducing AJ Gilbride, portrayed by Justin Long, a screenwriter facing serious allegations of sexual assault. A phone call from his team bears the shocking news that he’s been cut from their project. Although he vehemently denies these claims, his life begins to spiral downward, leaving him determined to seek refuge at another location – the very same Barbary House where Tess is entangled in her ordeal.
Upon his arrival, AJ finds Tess's abandoned luggage and is drawn to explore the basement. Before he can delve too deep, The Mother begins her relentless pursuit, driving AJ into a hellish pit where Tess waits, only to confront a similar fate.
The narrative rewinds back to the lively 1980s when Barbary Street was alive with activity. A man named Frank, played by Richard Brake, embarks on a quest for baby supplies, becoming fixated on a woman he encounters. Deceptively, he poses as an employee of the electric company to gain access to her home.
As the tension builds, Tess finds herself in a harrowing conflict, with AJ pleading for silence. A baby bottle is lowered into the pit where Tess struggles, consumed by fear while AJ shows reluctance to partake. The Mother’s seemingly nurturing side towards Tess clashes with her hostility toward AJ, resulting in a horrifying revelation as AJ finds himself compelled to suckle against his will. Tess exhibits incredible bravery, breaking the basement window just in time for Andre to rescue her as The Mother looms closer.
Although Andre tries to steer Tess away from the danger, her determination to rescue AJ leads her to contact law enforcement after unsuccessfully convincing Andre to help. The authorities, however, are dismissive, believing her disheveled appearance indicates substance abuse, leaving her without support.
As night falls, Tess sneaks back into the house to retrieve her vehicle keys. Just as she decides to escape, The Mother appears, attempting to force her way inside. In sheer desperation, Tess fights back, slamming her car into the house, momentarily stunning her pursuer.
Meanwhile, AJ stumbles upon Frank, nearing his end, in a separate room. Inside, he discovers distressing tapes that document Frank’s heinous acts against numerous women. Confronting Frank for his depravity pushes Frank to take his life, leaving AJ in shock. Rushing from the room, AJ hears Tess’s voice, leading to an instinctual gunshot that strikes Tess in the abdomen, yet AJ aids her escape regardless of their dire circumstances.
Finally, they reach the outside but realize that The Mother has vanished. Within a moment of fleeting hope, Tess reveals to AJ that she knows of a hidden sanctuary where they can find safety.
Guided by Andre towards a potential refuge, Tess learns the chilling backstory of The Mother—a product of Frank's grotesque legacy of abuse. With fear surging, Tess and AJ flee towards water's edge, only to find themselves terrorized as The Mother appears with harrowing swiftness, mercilessly tearing off Andre’s arm.
In a frantic bid for survival, Tess and AJ ascend a looming water structure. They narrowly grasp hope until disaster strikes when AJ negligently drops the gun. In a moment of warped redemption, AJ throws Tess to the safety of the ground, aiming to exploit The Mother's twisted instincts towards her perceived "baby."
Descending to find The Mother seemingly inert, AJ's moment of confrontation turns deadly as she awakens, inflicting horrific injury upon him. In a flash of brutality, Tess clutches the retrieved gun and, faced with the cycle of violence and horror, makes the harrowing decision to pull the trigger on The Mother, marking an end to this gruesome chapter. As she rises from the carnage, she sets off in search of medical aid, battered yet resolute.
