Colonel Sinclair arrives at a military facility to observe Colonel John Reynold’s experiment to control zombies created by the government’s use of “Trioxin,” a chemical developed in 1969 to destroy marijuana. However, scientists discovered Trioxin gas reanimated dead people, and these zombies could not be destroyed. They also craved human brains, and their victims became zombies, too. The ravaged zombies were placed inside barrels of Trioxin and moved to a secure facility where scientists sought ways to use them as military weapons. Sinclair proposed using an “exoskeleton” metal suit, but the military chose Colonel Reynolds’ “more humane” approach. At the laboratory, Reynolds discovers his key card is missing and borrows one from his supervisor, Colonel Peck. Meanwhile, the colonel’s son, Curt Reynolds, picks up his girlfriend, Julie Walker, and they use his father’s key card to sneak onto the base to observe the secret test. Inside the hangar, they see a technician tossing body parts into an incinerator. They move toward the laboratory, evade security by climbing atop of large metal crates, and watch the experiment through an overhead vent. Reynolds, Sinclair, and Peck observe from the control booth as a corpse is wheeled into the lab. A vent is opened on a Trioxin barrel, gassing the corpse, who comes back to life, screaming and violent. A technician shoots Colonel Reynolds’ weapon, which paralyzes the zombie and it “dies” again. Peck is excited by the experiment’s success, noting that cost-efficient “bio-units” could be sent into battle, then paralyzed and stored for future use. Julie is exhilarated, but Curt is upset and wants to leave. A guard hears them, and the couple quickly escapes. In the lab, the weapon’s effects are short-lived and the neutralized zombie returns to life and kills a technician. As other technicians scramble to shoot the zombie with the paralysis gun and strap him down, the dead technician reanimates and attacks. When the situation is contained, Colonel Sinclair reports on the experiment’s failure. Curt and Julie make love at the Reynolds’ home, and promise to stay together forever. His father returns home with news of his immediate reassignment to Oklahoma City. Curt angrily refuses to move with his father, and leaves with Julie. As they drive off, Curt swerves his motorcycle to avoid an oncoming truck, and Julie flies off the bike as he skids to a stop. Curt races back to help Julie, but she is dead. Heartbroken, he sneaks her body to his father’s laboratory. Unable to open a Trioxin barrel’s vent, he pulls off the top, unaware that a zombie is trapped inside. The Trioxin gas reanimates Julie, who feels numb and wonders what happened. As Curt explains, the zombie crawls from the barrel. Curt and Julie escape as a guard investigates the noise inside the lab. The guard sets off alarms before the zombie eats his brains. Colonel Reynolds learns of the crisis and returns to base. A scientist reveals Julie’s strong connection with Curt should keep her from attacking him until her brain shuts down. However, if she attacks, Curt will become a zombie, too. Sinclair wants to take command, but Peck lets Reynolds lead the search. Meanwhile, Julie is starving and Curt stops at a convenience store. Inside, gang members Santos, Mogo, Felipe and Alicia play video games. Julie frantically eats several snacks, but is not satisfied with anything. The gang taunts her, and when Curt warns them off, the thugs threaten him. The store owner grabs a gun from under the counter and orders everyone to leave. While Curt pays for Julie’s food, the gang robs the cash register and shoots the store owner. They turn on Curt, but Julie bites Mogo’s arm and eats some flesh. As the store alarm sounds, the gang runs outside and destroys Curt’s motorcycle before speeding away. The store owner begs Curt and Julie to drive him to a nearby hospital and they leave in his van. Police pursue them and the store owner wants to stop, but Curt refuses. The store owner opens the van back door to wave to police and they shoot, hitting him in the head. As the chase continues, Julie is attracted by the man’s blood and climbs into the back. Curt hides in an alley, and is shocked to see Julie eating the store owner’s brains. They escape into the sewer as police discover the van. When officers open the door, the zombified store owner attacks and kills one officer before Colonel Reynolds’ team arrives with the paralysis gun. Meanwhile, as Santos and his gang drive, Mogo’s wounded arm swells. Believing Julie gave him rabies, the gang determines to go after her. They see the van in the alley and know the sewer tunnel leads to a bridge over a nearby river. As Julie and Curt near the bridge, she pierces her skin with a wire spring and claims the pain helps curb her intense hunger. Curt is still in shock that she ate a man’s brain, but she claims it is his fault for bringing her back to life. He agrees death is a better alternative than being a zombie and she runs away from him. He follows her to the bridge and insists he did not mean what he said, but wishes things could be the way they used to be. She tells him that is impossible, and jumps off the bridge. Curt races to the river below, and is joined by a homeless man named Riverman. They find Julie’s body, and Riverman is stunned when she comes back to life. As the gang arrives across the river and threatens them, Riverman leads Curt and Julie deep into another tunnel and takes them to his makeshift home inside a pump room. Meanwhile, Colonel Sinclair arrives with orders to take command. However, Colonel Reynolds insists on saving his son, grabs the paralysis gun and leads a search team. Inside the pump room, Riverman offers to keep watch outside, while Curt and Julie rest. Both Curt and Riverman soon fall asleep, but Julie is starving and alleviates her pain by cutting and piercing herself. Mogo becomes increasingly sick as the gang searches the tunnels. They discover Riverman, and Curt runs to help, but is quickly overpowered. When Julie steps from the pump room, she is covered with stylized cuts and piercings, with nails and knives sticking out of her fingers and arms. Santos declares she is his type of woman and leads her back to the pump room. As Alicia notices that Mogo is dead, Riverman attempts to escape and Felipe shoots his leg. Suddenly, they hear Santos scream and Julie steps from the pump room, pulling his body by his partially detached head. Felipe shoots her, but it has no effect, and she kills him. She attacks Alicia, but Curt stops her. However, the dead Mogo reanimates, and kills Alicia. As the dead gang members reanimate, Curt, Julie and Riverman return to the pump room and board the door. Further down the tunnels, Reynolds and his men hear the commotion and rush to help. As the zombies attempt to break in, Julie begs Curt to tie her up because she is so hungry she might attack him. Riverman reveals a ladder behind the room that leads to the street, and Curt holds off the zombies while the wounded Riverman leaves with Julie. When the zombie gang breaks through the door, Curt outwits them and sneaks to the ladder, where he sees Julie eating Riverman’s brain. As she cries for him to end her pain, Curt is devastated and stops fighting as the zombie gang approaches. However, Colonel Reynolds arrives and paralyzes them and Julie. Later, after debriefing at the base, Reynolds offers to take his son on vacation before moving to Oklahoma City, and reveals Julie is now part of Sinclair’s exo-skeleton experiment. As Reynolds meets with Colonel Peck, Curt finds Julie locked in a cage. In an adjacent room, the zombie Riverman is attached to metal appendages and screams as Sinclair nails headgear into his skull. When a technician states that Julie is next, Curt frees her. Riverman goes wild, attacking the technicians and Colonel Sinclair. In the melee, Trioxin barrels are knocked over, freeing the zombies inside. As a lockdown commences, Julie and Curt attempt to flee. A zombie attacks, and Curt holds up his arm to protect Julie. Reynolds finds his son and tells him to save himself. Curt reveals his bloody arm. It is too late. Curt leads Julie to the incinerator, and they kiss as flames engulf them.