During the first outbreak of the Rage virus, Don (Robert Carlyle), his wife Alice (Catherine McCormack) and four others hid in a barricaded cottage on the outskirts of London. A frightened boy pounds on the door and they let him in, only to find that he is pursued by the infected. Most of the survivors in the house are killed, but Don, Alice, and the boy are chased upstairs. Alice will not leave the boy and Don escapes while his wife is dragged off. On a boat, Jacob the pilot (Shahid Ahmed) is taken too.
When the infected begin to die of starvation, NATO forces take over Britain. 28 weeks after the outbreak, American forces under Brigadier General Stone (Idris Elba) bring in settlers, including Don and Alice’s children, Tammy (Imogen Poots) and Andy (Mackintosh Muggleton), who were out of the country. They are all admitted to the Isle of Dogs, guarded by the U.S. Army, including sniper Sergeant Doyle (Jeremy Renner) and helicopter pilot Chief Flynn (Harold Perrineau). Tammy and Andy are reunited with their father, who lies about their mother’s death.
Andy dreams about forgetting his mother’s face, so he and Tammy sneak back into their former home to collect photographs. They find their mother alive and delirious. Taken back to District One, Alice is found to be an asymptomatic carrier. Don goes to her to apologize and kisses her. He is transformed by Rage, beats her to death, and infects thousands. General Stone orders a Quarantine and a Code Red Alert, which is basically kill everybody. A medical officer named Scarlet (Rose Byrne) rescues Tammy and Andy from the gunfire. Doyle will not fire his gun and escapes with them. Stone orders District One to be firebombed, but many escape. Children, they think, may hold the key to the future and must be protected.
Flynn arrives in a helicopter but will only take Doyle. Sam leaps aboard and falls, and everyone is abandoned. Flynn radios Doyle and tells him to go to Wembley Stadium. The others break into a Volvo to escape nerve gas. Doyle sacrifices himself by pushing the car and is killed by flame-throwers. Scarlet drives Tammy and Andy into the Underground, but Don kills her and bites Andy. Tammy shoots Don, but Andy may now be a carrier. Flynn flies them to France. 28 days later, the Rage virus is spreading in France.
Director Danny Boyle, producer Andrew Macdonald, and screen writer Alex Garland wanted to repeat the success of 28 Days Later with a sequel. Boyle picked Spanish filmmaker Juan Carlos Fresbatillo to direct and he re-wrote the script with Enrique Lopez-Lavigne and Jesus Olmo. They and Garland spent a year on it. The film was well-received as a terrifying thriller.
All the actors playing the infected were required to have a movement-based background—ballet, dance, gymnastics, circus performing or mime—to create the bizarre movements necessary. A 28 Months Later was never made, though they are still talking about it. The farm where Don and Alice hide out was also in Children of Men. The last shot, in Paris, was added at the last minute. The night scenes were shot in the daytime because buildings that are supposed to be abandoned would have lights in them at night but shooting in the daytime and darkening the film digitally would solve that problem. It gave the scenes a ghostly quality.