A young girl returns home to find her parents missing and the house in disarray. She sits down to watch television, and the news reveals that five years earlier, a zombie outbreak killed off 4.5 billion people worldwide, 10 million of which are from the United States. After detonating a nuclear bomb over San Francisco and walling off New York City, the U.S. government declared the outbreak over and established a paramilitary force known as R-Division to hunt down and destroy the remaining zombies. The show she’s watching, called Re-Kill, broadcasts live footage from R-Division squads, with commercials interrupting the action to show efforts to repopulate the country and reassure the public.
The embedded journalist accompanies a squad on a raid to New Orleans, where reports of zombie activity surface. The mission goes disastrously wrong, and only two reach a car: Alex Winston and the journalist. When the journalist’s voice falters and she moans, Winston realizes she is infected and shoots her. The government publicly claims the outbreak is under control, and Winston is reassigned to Division 8, a unit built around a new roster: a fresh recruit, Tom Falkirk; a former thief, Omar Hernandez; an immigrant, Nguyen; Rose Matthews, Grizzly Adams; conspiracy theorist Trent Parker; and their squad leader, Sarge.
Along with embedded journalists Jimmy and Bobby Camera Guy, Division 8 is sent to investigate reports of a family harboring reanimated relatives. [Sarge] explains that the outbreak spread in part because people clung to the hope that loved ones could be saved. After neutralizing the human resistance, the squad rescues prisoners kept chained for zombie food. One family member reveals that his sister, a zombie, is kept in the attic. Before she can be put down, she bites Tom Falkirk, who is mercy-killed to prevent his turning. In interviews, Parker is dismissive of Tom’s sacrifice, and Sarge notes that such risks are an accepted part of the job.
Division 8’s next assignment leads them to a truck suspected of carrying contraband. When they stop the vehicle, it’s full of zombies. Sarge uses a rocket-propelled grenade to clear them out. The truckers claim ignorance about their cargo but eventually confirm rumors of the Judas Project, a shadowy program said to test the zombies trapped in New York City. Parker believes it to be a secret military operation, while Sarge worries about a second outbreak—an inevitability, he argues, given human nature.
In The Zone, the forbidden heart of New York, they encounter dead scientists and zombies who appear more intelligent. After an ambush, Omar insists that Parker was bitten and urges the group to kill him, but Parker opens fire and kills Adams. Winston is wounded and sacrifices himself with a grenade to allow the others to escape. A previously recorded interview shows his belief that the government has secretly prepared an ark for eligible survivors, and he posthumously wishes the squad well.
Deeper in the Zone, Hernandez is bitten and turns. As the squad fights a horde, a man claiming to be the last member of the Judas Project leads them to safety, but Nguyen is left behind and killed. The project’s purpose is revealed to be turning zombies against one another, yet it exposes an alpha zombie nicknamed Elvis who can rally the undead. Jimmy reports that the network drones will broadcast his and Bobby’s footage every two hours. As reconnaissance continues, Bobby dies, alerting the zombie army. The squad flees, but Sarge and the Scientist are killed by the oncoming horde. Elvis appears and kills Jimmy, then throws Rose a window; he tries to strangle her, but she kills him and escapes The Zone. A special news report reveals zombie activity near the Zone and the start of a new outbreak, and the young girl who started all this is shown to have transformed into a zombie. Elsewhere, the ark is confirmed to be real, and soldiers, including Rose Matthews, discuss having found groups of survivors.