Zoe Hull, portrayed by Isabel May, is struggling to navigate the unforgiving terrain of high school life after the heart-wrenching loss of her mother, Jennifer. The bond with her father, Todd, played by Thomas Jane, has grown tenuous, leaving Zoe feeling isolated and unsupported. One fateful day on her way to school, she inadvertently stumbles upon a bizarre event involving Chris Jelick, portrayed by Britton Sear, who mischievously plants a mysterious device in a field, which Zoe brushes off as just another high school prank.
As the school day unfolds, her friend Lewis, played by Olly Sholotan, attempts to gather the courage to ask Zoe to prom, but she recoils in embarrassment after an accidental spill of her drink sends her rushing to the restroom for solace. Meanwhile, chaos erupts within the community as a series of explosive devices go off, drawing emergency services away from critical locations.
The situation escalates dramatically when a van crashes into the school cafeteria, bringing with it a group of armed intruders—Tristan Voy, played by Eli Brown, Chris Jelick, along with Anna Jelick, portrayed by Catherine Davis, and Kip Quade, played by Cyrus Arnold. As the orchestrator of the violent siege, Tristan commands his cohorts to start targeting students, but many find themselves trapped and overwhelmed by the sheer number of attackers. In the midst of terror, Lewis takes charge of the school's Facebook page to broadcast the unfolding horror live. Using her ingenuity, Zoe cleverly escapes through the bathroom ceiling, attempting to alert her classmates and guide them to safety.
Amidst the growing tension, Tristan tries to manipulate the school's front office by falsely reporting the shooting, but the established protocols hinder his sinister intentions. The principal and the security guard rush to the scene, only to uncover that Tristan's plot is a desperate bid for notoriety, which culminates when he coldly kills the principal, all while letting the unarmed guard slip away, mocking him for his lack of preparedness. The school then goes into lockdown as the gravity of the situation sinks in.
Sheriff Tarsy, played by Treat Williams, frantically attempts to manage the escalating crisis, but a devastating explosion claims the life of the first arriving officer. In the chaos, Anna begins to survey the wreckage while Zoe deduces that the shooters aim to enforce lockdown measures to isolate their victims further. Despite her best efforts to warn fellow students, Anna intercepts her, leading to a gripping confrontation where Zoe acts in self-defense, fatally wounding Anna with her own weapon.
Meanwhile, a police officer uncovers the grim scene at Tristan's home—his mother has been brutally slain. As news spreads of the violence, Tristan basks in the notoriety spawned from the tragic events, rounding up students hiding in their classrooms. When Kip's confession reveals the deep-rooted resentment that fueled his actions, stemming from past bullying, Zoe realizes the weight of the situation. She makes a crucial call to Sheriff Tarsy, planning a distraction to facilitate the students' safe evacuation while maneuvering media coverage away from the school.
Yet, during a live discussion with Sheriff Tarsy, Tristan begins to sense Zoe's deception and demands her immediate surrender, threatening to execute hostages every five minutes. In a bizarre turn of fate, Zoe returns to the remorseful Kip, convincing him to help set a trap for Tristan and Chris, leading to Kip’s tragic downfall amidst the chaos. As bullets fly, Zoe tends to an injured Lewis, confessing her long-hidden feelings for him, though her anxiety about the situation around them momentarily overshadows this revelation.
The cafeteria becomes a perilous battleground as Chris is poised to detonate an explosive-laden van, a plan foiled by Todd’s sharpshooting from outside. In a bold move, Zoe commandeers the livestream, declaring that her legacy will overshadow Tristan's. Shockingly, as Tristan rigs the van to explode, he manages to escape with a hostage. Anticipating his move, Zoe expertly maneuvers the van into reverse, leading to a catastrophic explosion that engulfs the vacant lot.
In the aftermath of the disaster, Zoe pursues Tristan, only to be mistakenly apprehended by SWAT. Outside the school, Sheriff Tarsy congratulates Zoe for her bravery, revealing that Tristan has met his end in flames. With the dust settling, Zoe reunites with her father, beginning to mend their bruised relationship. Nevertheless, a sense of dread lingers when Zoe glimpses Tristan, having faked his death, fleeing into the woods. Armed with her father's hunting rifle, she confronts him in a final showdown, ultimately allowing him to succumb to his injuries while condemning him for his horrific deeds.
