A SWAT team storms a school library, finding a student wielding an axe and surrounded by gruesome scenes of violence, before the narrative rewinds eight hours earlier. Crestview Academy holds Saturday detention for six unruly prep school students, with psychologist Dr. Day (Jeffrey Schmidt) conducting psychological assessments to unveil the students' personalities, meticulously documenting each session. After receiving an expulsion notice from Headmaster Nash (Judd Nelson), newcomer Matt Clark (Cameron Deane Stewart) aims to amend his reckless behavior by joining a motley crew in detention. This group includes the socially awkward Tarek Ahmed (Marc Donato), athlete Craig Cook (Roger Edwards), the cunning Goth girl Veronica Harmon (Augie Duke), the prim and asthmatic Megan McDurst (Amanda Alch), and the popular Tricia Wilkes (Ali Faulkner).
Dr. Day sets them to work on a history assignment, isolating them by restricting internet access and collecting their phones, ultimately leaving the students trapped in the library, which takes on a peculiar atmosphere adorned with Native American portraits and an Apache statue, thanks to the janitor, Max (Ben Browder). The students feel an eerie presence within the space. As they share their dysfunctional family backgrounds, tensions arise stemming from their past encounters, while they attempt to escape the library to no avail. In a reckless episode, Veronica hides Megan's inhaler, leading to disastrous consequences, as Megan gasps for breath and tragically dies before help arrives.
With the internet operational again, Veronica ventures into research, uncovering a narrative about a deceased individual, Jacob Rainwater, whose land was usurped by General Andrew Winston Clarke and later appropriated by Crestview for the school's construction. As arguments flare, they discover a pathway through the vents, which connects different locked rooms, intensifying suspicions towards Matt, who conceals a troubled past. When Tarek disappears, they return to the library, revealing connections that intertwine their families with the legacy of Rainwater, uncovering that powerful figures—including Tricia's mother, the Governor—colluded to allow their children privileges to ensure their graduation.
The school spirals into chaos as a raging storm disrupts power, amplifying their fears of the supernatural. In a horrifying accident, Craig tumbles down the library stairs and meets his demise when one of his crutches impales him. Tensions rise as Tricia confesses her family's role in Jacob's demise; with frantic intentions, Veronica attempts to contact Jacob's spirit, ultimately leading to a tragic outcome when she takes her own life out of fright after facing the spectral entity.
Dr. Day, revealing his sinister alliance with Veronica, has orchestrated the group's panicked responses, manipulating their emotions for profit, then violently ends Tarek's life to fuel their terror. As the situation escalates, he turns against Veronica, killing her when she attempts to confront him with a nail gun. The ensuing turmoil leads to Matt being wrongfully blamed for all the carnage, only for the situation to take a twisted turn when a trap kills Dr. Day.
Ultimately, a beleaguered SWAT team finds Matt, now a suspect with an axe in hand, while revelations ensue as Max reveals his ancestry connects to Jacob Rainwater's legacy. The movie closes with Matt being led away in an ambulance, as key figures involved in this dark history buy their way out of accountability, leaving a chilling aftermath behind.
