Four weeks after a mysterious, incurable virus spreads throughout the UK, a handful of survivors try to find sanctuary.

A group of animal rights activists break into a lab and release monkeys from their cages to rescue them, despite warnings from a scientist that the monkeys are contagious. As a result of the animal rights activists' actions, a virus that the monkeys contained rapidly across Great Britain and infects numerous people. Jim, who fell into a coma following a bicycle accident shortly before the virus was released, emerges from his coma and finds that London is deserted.

He realizes that he is not alone, as within the city there are those that have been infected and those that have not. Jim manages to find more survivors and they head out to Manchester, where a group of British military personnel offer protection of any survivors from the infected. However, Jim and his colleagues have no idea what they're in for.