Nearly three decades after the rage virus escaped a British lab, a small community survives on Holy Island, a tidal island cut off from the mainland by a causeway that floods with every tide. Jamie lives there with his wife Isla, who suffers from a mysterious illness that leaves her in pain and confused, and their 12-year-old son Spike. When Jamie takes Spike to the mainland for his first hunt, the boy sees the truth of the world: infected that crawl and eat worms, and worse, towering "Alphas" that run like athletes. After Spike makes his first kill, he catches his father with another woman. Heartbroken and angry, he sets a fire as a diversion and sneaks his mother across the causeway to find Dr. Kelson, a healer rumored to live on the mainland. On the journey, Isla briefly becomes her old self near the Angel of the North, then slips away again. At a ruined gas station (its sign missing the S, so it reads "hell"), they meet Erik, a stranded Swedish sailor, who saves them from a horde by blowing up the gas-filled building. Later, inside an abandoned train, they find a pregnant infected woman in labor. Isla helps her deliver a healthy, uninfected baby girl. When Erik tries to kill the child, a massive Alpha named Samson rips his head and spine out in one motion. Dr. Kelson arrives, calms Samson with a morphine dart, and takes the trio to his home: the Bone Temple, a monument of over 250,000 cleaned bones and 5,500 skulls built to honor everyone the virus killed, infected or not. Kelson examines Isla and gently tells Spike the truth: she has terminal cancer that has spread to her brain, and nothing can save her. Isla chooses a peaceful death, and Kelson euthanizes her while Spike is sedated. He gives the boy her cleaned skull to place at the top of the temple, teaching him "memento amoris" - remember, you must love. After a final fight with Samson, Spike takes the baby back to the island, leaves her at the gate with a note naming her Isla, and walks back into the mainland alone. His father Jamie runs to the causeway but the tide has already blocked him. Twenty-eight days later, Spike - now a harder, skilled survivor - is cornered by a pack of infected. At the last second, a bizarre gang rescues him: men in velvet tracksuits, bleached wigs, and gold chains, led by a grinning man who calls himself Sir Jimmy Crystal. Jimmy, we realize, is the child from the film's opening scene, who watched his family die while the Teletubbies played. He welcomes Spike into his club. The film ends there, setting up 28 Years Later: The Bone Temple.

The ending reveals two things at once. First, the infected have become part of nature: they can breed, their children can be born uninfected, and the "placenta" protects the baby - a hint that the virus is becoming something new rather than simply dying out. Second, the real future threat may be human. Sir Jimmy Crystal is the little boy from the opening, whose father welcomed the infected into his church believing it was the second coming. His gang, the Jimmies, dress like a warped children's TV memory (their outfits nod to the disgraced UK TV star Jimmy Savile, a deliberate and dark British joke). The upside-down crosses and Teletubbies colors mark a childhood frozen at the moment of trauma. Spike joining Jimmy is not a happy ending - it is a warning. The sequel, 28 Years Later: The Bone Temple (released January 2026), picks up exactly here, with Spike inside the cult and Kelson discovering something that could make the apocalypse even worse. There is no post-credits scene; the film itself is the cliffhanger.