About eight years after a catastrophic zombie apocalypse, the story revolves around R, a zombie portrayed by Nicholas Hoult, who spends his days aimlessly wandering through an airport now overrun by hordes of the Undead, including his best friend, M. R and M communicate in a primitive manner filled with grunts and occasional near-words, trying to navigate their new existence. As a zombie, R grapples with an insatiable hunger for human flesh, particularly brains, relishing the memories of his victims, which allow him to feel a semblance of life.
Within this world, there exists a terrifying breed known as the Boneys—zombies so devoid of flesh that they will consume anything alive, posing an even greater threat. During a hunt for food, R and a group of zombies encounter Julie Grigio, played by Teresa Palmer, along with her friends. This group is on a mission sent by Julie’s father, Colonel Grigio, portrayed by John Malkovich, to fetch medical supplies from abandoned structures.
R becomes infatuated with Julie upon seeing her. In a chaotic turn of events, he kills her boyfriend, Perry, after being shot by him, consuming Perry's brain which deepens his feelings for Julie. To ensure her safety, R cleverly masks her scent with zombie blood and takes her to his makeshift home in an airplane at the airport.
Though initially fearful of R and questioning his motives, Julie gradually starts to trust him after he helps her during a desperate escape attempt. They bond over LP records and games, with R experiencing a slow revival of his humanity alongside their growing connection. However, as time passes, Julie becomes restless and attempts to return home, attracting a horde of zombies in the process. R heroically intervenes, but the struggle forces him to confront the painful truth that he was responsible for Perry's death, leading Julie to flee back to her home.
Heartbroken, R meanders back to the airport, only to discover that he and M, along with other zombies, are beginning to rediscover their lost humanity. But the Boneys, relentless in their hunt, become a looming threat. R and M rally a group of zombies and venture to the human enclave, where R secretly infiltrates the fortified community seeking out Julie and her friend, Nora.
At first shocked, Nora becomes an ally when R reveals the remarkable transformations occurring among the undead. However, Colonel Grigio remains skeptical and aggressive toward R until Nora intervenes, drawing a gun on him. The tense situation escalates, culminating in a frantic escape to a baseball stadium, where they unexpectedly face an onslaught of Boneys.
As R and Julie are cornered, they find themselves with no choice but to leap into a pool to evade capture. R fortifies Julie's fall with his own body, showcasing his newfound protective instincts. When Julie manages to pull R from the depths, their burgeoning romance culminates in a kiss. Suddenly, the Colonel appears and shoots R, prompting Julie to advocate for his humanity just as R's injury reveals a shocking turn: he has fully transformed back into a human.
The climax witnesses a united front of humans and zombies fighting against the Boneys, leading to their annihilation and the gradual integration of zombies into human society. The film concludes with a transformed R and Julie standing hand in hand, watching as the wall encircling the city is demolished, symbolizing a hopeful new beginning after the apocalypse.
