At a bar, Deb Clarington, a camera operator for the local news, spots a tall, attractive man Ryan Waverly across the room. Her nerves fade when her friend Ruby encourages her to say hello. The moment is interrupted by Ryan's fiancé, who breaks up with him after he refuses a high-paying job at his father's company. Deb then wakes up later in Ryan's bed with a heavy hangover. Ryan asks her to leave, and after several awkward attempts to seduce him, she reluctantly heads out but soon witnesses people attacking and cannibalizing each other. Deb dives into the chaos to save [Ryan Waverly], pulling him back to his apartment and away from the rising tide of danger.
Back inside, Deb tries to win him over again, while Ryan focuses on checking in with his family and ex-fiancée. With no car to escape, Deb offers to help him navigate this unfolding crisis. They first visit his elderly neighbor to gather supplies. The neighbor appears dead, only to rise again as a zombie. They kill her, but the noise and chaos draw more undead. The pair drop the supplies, triggering a new stampede, and race back to Deb's car, vowing to push on toward Ryan's family. Deb eagerly rams through clusters of zombies, while Ryan objects, suggesting that some may still be treatable and urges restraint. Despite the tension, Deb agrees not to waste effort on needless killings.
Their plan is interrupted when Deb detours to visit Ruby, who has become a zombie, and she traps Ruby in the car trunk, hoping to study a possible cure. At Ryan's father's mansion, they are admitted by Chaz Waverly, Ryan's brother, who quizzes them about whether they are zombies before letting them in. Inside, Ryan is reunited with Stacy, and Frank Waverly reveals that his water treatment plant has spread the virus to town. When Deb presses for more details, Frank deflects blame onto the governor for backing an environmentally dangerous project, which deeply disturbs Ryan.
Frank privately tells Ryan that the governor has arranged helicopter evacuation, but Ryan insists Deb accompany him. Frank resists, then relents when Ryan threatens to stay behind. He tries to drug Deb to abandon her, but Deb outsmarts him by handing the drugged food to their security guard. A tense turn of events follows: Ryan tells Stacy he no longer wants to marry her, and she tries to provoke jealousy by simulating sex, triggering intense strain. After the guard dies, zombies overrun the mansion; Stacy is eaten alive, and Chaz is stunned into inaction, ultimately allowing himself to be bitten. The Waverlys escape the mansion with Chaz in tow, heading toward a potential helicopter escape.
Deb discovers a security checkpoint at the town’s edge and is allowed to leave, but is warned to turn back later. She invokes Frank’s name to the governor, who reveals there was never any helicopter—only a cleanup plan with darker motives. Ryan confronts the governor and reveals that Deb is a reporter carrying crucial evidence in her car’s trunk; the governor opens the trunk and Ruby kills him. When Frank is bitten, he urges Ryan and Deb to flee while he holds off the soldiers.
Back in town, Deb realizes they can broadcast from her television station so their message cannot be jammed. She proclaims her love for Ryan Waverly on air, then is bitten. Believing she is turning, she begs Ryan to leave her behind and wait for help, but he refuses and offers himself as zombie fodder. Before he can be bitten, paramedics burst into the station and reveal that the virus is not contagious. Frank and Chaz, who have also survived though under arrest, urge Ryan to declare his love for Deb. As fighter jets hammer the city from above, the pair share a final kiss, clinging to hope that love and resilience can endure the nightmare.
