Russell Curran, portrayed by Brendan Fletcher, is a prosperous businessman settled in Portland, Oregon. His wife, Lauren Curran, played by Christina Ricci, contends with bipolar disorder, a condition that surfaced after a traumatic home invasion where she suffered injuries and lost their baby, drowning in the bathtub.
In search of a sanctuary, Russell and Lauren opt to relocate to a lavish, cutting-edge smart apartment located an hour away from Portland. During one of their initial evenings there, they join a cocktail party and mingle with the affluent residents, including Phillip Starks, an heir to a successful marketing firm that specializes in consumer psychology, embodied by Vicellous Reon Shannon.
However, Lauren soon begins to hear odd noises emitting from the apartment's sound system and glimpses unusual images flashing across their television. When she tries to discuss these disturbances with Russell, he dismisses her concerns, attributing them to her mental health struggles and accusing her of being paranoid. As the situation escalates, Russell covertly installs CCTV cameras to monitor Lauren’s behavior, further increasing her sense of isolation.
Through a series of internet inquiries, Lauren connects with John Cusack, a hacker and journalist named Vernon Sarsfield. Vernon validates Lauren's fears, informing her that she is not delusional. He believes she can assist him in unveiling a sinister truth: the residents are unwitting subjects in a gruesome experiment involving subliminal messaging conducted by the apartment's owners. He suspects Lauren’s heightened awareness is due to her bipolar disorder.
The tension rises when Lauren meets a fellow resident who has always seemed oddly out of place. He confesses to her that he "is not one of them" before tragically taking his own life by jumping off the building's roof. As the occurrences become increasingly bizarre, Vernon urges Lauren to escape, revealing he has been tracked and can no longer offer his protection.
Lauren’s distrust toward Russell intensifies as he threatens her with institutionalization. Noticing that all the residents are incessantly scratching their necks, she deduces that they are potentially exposed to a substance or implanted device. In a desperate bid to flee, she is intercepted by the building’s security manager and groundskeeper, who subsequently restrain and sedate her.
Upon regaining consciousness, Lauren finds herself restrained and bombarded by yet another subliminal message on the television, compelling her to commit murder against a three-year-old child residing in the building. Just then, Vernon appears, freeing her from her bindings. He hands her a gun, allowing her a moment to escape by confronting their pursuers, sacrificing himself in the process.
Under the influence of the implanted imagery, Lauren abducts the child. Russell attempts to regain her confidence, asserting he has evidence of the subliminal manipulation through the footage captured by the CCTV cameras, but she rebuffs him sharply. Driving the child to a secluded shack, she later heads to an opulent but abandoned hotel, where she has a chilling meeting with Phillip Stark and the building’s staff, who turn out to be his accomplices.
During her interview with Stark, he inquires about her feelings regarding what she has done. Lauren, seemingly following the expectations set before her, declares she feels well, which pleases Stark as he sees potential in her for future endeavors in warfare.
Just when Stark opens a bag that supposedly contains the child's remains, it is revealed to be filled with apples instead. A flashback uncovers the truth: Lauren and Russell had been acting, soullessly faking the child's death. A confrontation ensues when Stark turns violent, only for Russell to intervene, fatally shooting Stark as law enforcement descends on the scene.
In the film’s concluding moments, a pregnant Lauren and Russell begin anew in a different home, embracing each other. Yet, a flicker of suspicion lingers in Lauren’s gaze as she notices the parent unit that Russell has been attempting to install, hinting at unresolved tension and uncertainties in their new beginning.
