After breaking into a primate research facility, a group of animal rights activists discover caged chimps chained up before banks of screens displaying horrifying, violent images. Ignoring the warnings of the terrified researcher who maintains that the chimps are infected, they begin to free the animals and are immediately subjected to a bloody attack from the enraged creatures. Twenty-eight days later, Cycle courier Jim awakes from a coma in the deserted intensive care unit of a London hospital. He wanders out into a church where he finds dead bodies piled in heaps on the chapel floor. A sudden explosion from a makeshift bomb heralds the arrival of fellow "survivors" Selina and Mark. They take Jim to safety and explain to him that this infection is transmitted by blood and overwhelms the infected victim with a murderous rage within seconds. Britain has been overrun, and they have no way of knowing if it has spread worldwide. Their only hope of survival may lie in the hands of a Manchester group of soldiers, as they claim to have the "answer" to infection and invite any survivors to join them at their blockade. Faced with no practical alternative, the group sets out northwards, unaware that the worst is yet to come.