In the heart of New York City, a teacher named Ms. Daigle finds herself returning to her dim and unsettling apartment building, which is managed by her landlord, Mr. Johnson. Her day takes a strange turn when he informs her that a master key has gone missing and that all locks need to be replaced. Upon entering her apartment, she discovers that her friend Ann has vanished, leaving behind a note that indicates she had to leave unexpectedly. Additionally, she finds Brad, her disabled student, who relies on her care. After attending to him, Ms. Daigle grades papers with a red pencil while a hidden camera records the events unfolding in Brad's room. The tension escalates when a sudden image flashes on the screen, prompting Brad to scream and cling onto a cluster of keys, which he refuses to relinquish. Things take a darker turn as Ms. Daigle becomes the target of vicious attacks, culminating in her being stabbed with her own red pencils.
The narrative shifts to Phil, who arrives at the building with his two daughters: Violet, played by Taylor Richardson, a sullen teenager grappling with her mother’s death, and Rose, his younger daughter, who brings a sense of innocence to the story. Phil tells the girls to wait in the lobby while he speaks with Mr. Johnson about applying for the superintendent position. He hopes this job will afford him more time with his daughters, particularly after the tragic loss of their mother. As the conversation unfolds, Mr. Johnson provides a glimpse into the building's history, revealing its origins as a failed savings and loan during the Great Depression. The building houses a blend of affluent and low-income apartments, combined with a confusing basement maze and an antiquated furnace from the 1890s.
In the lobby, they encounter the cantankerous Mrs. Grey, who is delighted to see Violet engrossed in a book by George Bernard Shaw. Meanwhile, young Rose, restless with her toy, begins to explore her surroundings. As Violet wanders off and meets a boy named Vondell, who introduces her to smoking, Rose's curiosity leads her to the basement, where she has a chilling encounter with Walter, the unsettling janitor who warns her that she should not be there.
As Phil begins unpacking the family’s belongings in their poor-quality apartment, he quickly realizes that its condition is only temporary. Despite the new environment, Violet remains discontented, especially after the shocking news of Ms. Daigle's murder, who was one of her favorite teachers.
Mrs. Grey becomes increasingly suspicious after hearing strange noises and arming herself with a knife, only to vanish under mysterious circumstances, adding to the building's ominous atmosphere. One day, while taking out the trash, Phil stumbles upon a bag from Ms. Daigle’s apartment filled with her broken red pencils, raising further alarm.
Phil’s interactions with Julio, another employee of the building, provide both aid and complications. While Julio attempts to help furnish Phil's apartment, he also exhibits questionable behavior that raises Phil's protective instincts. As the tension escalates, the strange disappearances within the building start making headlines, and Phil’s worry for his daughters intensifies.
Violet's peril deepens when she finds herself trapped in a malfunctioning elevator controlled by Walter, whose unsettling gaze monitors the residents of the building. As Phil becomes increasingly suspicious of both Mr. Johnson and Walter, he takes drastic steps to ensure his daughters' safety and begins to uncover the dark secrets of the building.
As the series of mysterious events unfolds, family dynamics intensify between Phil and Beverly, a striking woman he encounters during a party. Beverly understands Violet's struggles, drawing connections to their respective pasts. However, the atmosphere shifts when secrets emerge, revealing that Violet and Rose are twins who share a haunting history, like the tragic fire that claimed Rose's life.
In a race against time, chaos ensues in the building with suspicious figures disappearing one after another. With rising adrenaline, it becomes a desperate collision of violence and mystery as Phil confronts Walter, triggering a series of frantic encounters that lead to a shocking revelation about what lurks within the building's depths. The story culminates in a dramatic and unsettling sequence that leaves the audience questioning the very nature of safety and familial bonds in a place fraught with darkness. As the tale unfolds beneath the shadow of danger, who will survive and who will become a victim of the eerie depths of their new home?
