The film opens with Simon (Tyron Leitso) and Greg attempting to set sail to an island rave party. They are joined by Alicia (Ona Grauer), Karma (Enuka Okuma), and Cynthia (Sonya Salomaa). While Karma has her sights set on Simon, he is infatuated with Alicia, and Cynthia is in a relationship with Greg. Upon reaching the dock, they discover the boat they intended to take has already departed. Consequently, they hitch a ride with Victor Kirk (Jürgen Prochnow) and his assistant Salish (Clint Howard). Their journey is interrupted by Jordan Casper (Ellie Cornell), a police officer attempting to halt them due to Kirk's dubious activities as a smuggler, but they proceed regardless.
Upon arrival at the island, they are met with a disheveled rave site devoid of partygoers. Alicia, Karma, and Simon begin a search for the others, leaving Cynthia and Greg behind. In the heat of the moment, Greg steps away to relieve himself, leading to tragedy as Cynthia is brutally killed by a horde of zombies. Meanwhile, the trio discovers an abandoned house occupied by survivors Rudy (Jonathan Cherry), Liberty (Kira Clavell), and Hugh (Michael Eklund), who explain that zombies have overrun the rave, slaughtering everyone present. They quickly return to find Cynthia but learn she has transformed into a zombie herself and mercilessly attacks Hugh before being shot by Casper.
Faced with overwhelming odds, the group devises a plan to escape the island using Kirk's boat, only to find it besieged by zombies. Casper and Greg venture out to seek help but are ambushed, resulting in Greg's death. In a desperate measure, Kirk leads the group to a stash of weapons he's been smuggling so they can defend themselves. Armed and ready, they return to the house, where a chaotic gunfight ensues, reminiscent of a video game, pitting the armed teens and Kirk against waves of zombies. During the frenzy, Liberty and Casper fall, while the remaining survivors manage to enter the house.
As the chaos escalates, Kirk hears Salish whistling outside and, in a tragic twist, encounters him as a zombie. Although he shoots Salish, Kirk is bitten and ultimately resorts to suicide, detonating explosives that flood the house with zombies. The four teenagers retreat to a lab, but their sanctuary is breached. In a moment of bravery, Karma discovers a hidden trapdoor, allowing Alicia, Rudy, and herself to escape as Simon sacrifices himself by igniting a barrel of gunpowder, obliterating the house and many zombies.
Navigating through a series of tunnels, Karma heroically fights off zombies while covering her friends’ escape but is ultimately overwhelmed. Alicia and Rudy find themselves captured by Castillo, a man who has injected himself with an immortality serum and inadvertently birthed the first zombie. They manage to flee, inciting an explosion that collapses part of the tunnels, but Castillo pursues them. In a harrowing duel, Alicia is mortally wounded, but Rudy decapitates Castillo, only for the headless body to attack him. With her last ounce of strength, Alicia crushes Castillo's head, seemingly succumbing herself.
In the aftermath, Rudy and Alicia are rescued by federal agents who eradicate the remaining zombies. The closing narration reveals that Rudy administered the immortality serum to Alicia, ensuring her survival but also sealing her fate as she is now infected and destined to become a zombie in time.
