In the near future, humanity has been ravaged by a disease caused by a
parasitic fungus transmitted by bodily fluids. Over the prior decade, most of humanity that was infected turned into fast mindless zombies called "hungries". The only remaining hope is a cure that could be obtained from research on a small group of carrier but apparently normal children. The children are imprisoned by a group of soldiers led by Sergeant Eddie Parks, and go to school at an army base in the
Home Counties, where they are experimented on by Dr. Caroline Caldwell. Helen Justineau is responsible for educating and studying the children. Among them is an exceptional girl named Melanie, whom Justineau grows particularly close to, thus forming a special bond. When Melanie is about to be dissected, the base is overrun by hungries and the operating lab is breached. Melanie escapes and wanders outside, where soldiers are being violently attacked. Melanie and Justineau board an escaping truck with an injured Caldwell, Sergeant Parks, and two surviving soldiers, Gallagher and Dillon. Melanie is restrained and muzzled to prevent her from biting the others. Dillon is killed when hungries attack as the group stops for water, and the truck is disabled when a fuel line is broken. The group reaches
London by foot and makes their way through a swarm of dormant hungries using a "blocker" gel that masks their scent, rendering them largely invisible. They take shelter in an abandoned hospital for the night. Caldwell reveals to Melanie that second-generation hungries, or neonates, were discovered after babies killed their infected mothers by eating organs to get out of the womb, and while they crave living flesh, they still think and learn, as the fungus has a symbiotic relationship with those born infected. In the morning, the group realises they have been surrounded by hungries. Melanie, as a second-generation hungry, is ignored by them and therefore goes to explore abandoned houses, eating a stray cat during her time out. She helps the group by leading the hungries away with a stray dog so the group can escape. As they progress through London, they come across piles of infected bodies encircling the
BT Tower, which has been overgrown by a massive fungal growth. Caldwell explains that the growth contains pods which, upon maturity, could release airborne spores that would end humankind. They take shelter in an abandoned mobile laboratory that was sent into the city earlier by the military authorities. Caldwell, injured and dying of
sepsis, reasons that she can save the human race by sacrificing Melanie to complete her vaccine research in the lab. As the group runs out of food, Gallagher ventures into the city on a supply run, but is killed by a tribe of feral hungry children who have learned to trick uninfected people with a trail of food cans. When Parks and Justineau are surrounded by the feral children, Melanie fights and handcuffs the leader and kills him with a bat. The remaining children back off, allowing the group to escape. Caldwell attempts to dissect Melanie upon the group's return to the lab, imploring her to sacrifice herself for Justineau. Melanie comes to the realisation that she is not an experiment and that her kind, human-zombie hybrids, will be the future of the world. She escapes and sets the towering pod structure alight, causing it to release an immense cloud of spores. Caldwell chases after her, but is killed by the tribe of children. Parks leaves the lab in search of Melanie, but becomes infected by the spores. He hands Melanie his gun and tearfully asks her to shoot him, as he does not want to turn into a hungry. Melanie obliges and shoots Parks as he is about to turn. In the lab, Justineau stands inside the sealed door, watching the spores fall. The film ends with a tearful Justineau, safe but confined to the sealed mobile lab due to the lethal spore-filled air. Outside, the hybrid children of the army base, along with the feral children, sit together, kept sternly in place by Melanie. Justineau speaks through a microphone, educating the newly-dominant human-zombie species. ==Cast==