NOTE: This spoiler sent in by Marcus.
The film begins with Alice (Catherine McCormack) and her husband Don (Robert Carlyle) making food in a dark cottage. The infection of the Rage virus has happened recently, and they managed to escape to the countryside. Don and Alice are grateful that their children are on a school trip outside of Britain, and are not infected. They passionately kiss each other when an old woman interrupts them. The cottage is owned by her and her husband, and all the windows have been boarded up. Don and Alice prepare a meal for the elderly couple, a woman, and Jacob (Shahid Ahmed). Over dinner, the other woman wants there to be a place set for her boyfriend, but Jacob tells her that he’s been gone for a while and he’s not coming back. Suddenly, there’s a lot of banging on the front door. It’s a little boy, who hasn’t been infected. After debating, Don lets him in and quickly shuts the door. They feed the boy, asking where he came from. He says that he came from a neighboring town, and that his family is chasing him. When the other woman looks outside, she is startled by an infected, who breaks through the boarded up windows and vomits blood onto the woman’s face. Don beats the infected woman to death with a crow bar. Quickly, the other woman becomes infected and Don kills her as well. Several infected people burst through the cottage while the survivors frantically try to run away. The little boy runs upstairs and Alice runs after him while Jacob and the elderly couple run to the barn. The old man tries to hold the door shut, but the infected break through and give him the virus. The old woman is viciously killed by the infected as Jacob makes it outside and runs away. Don runs upstairs and tells Alice to leave the boy, who’s hiding in the closet. An infected comes between Alice and Don. Alice screams for Don to help her, but he cowardly shuts the door and jumps out a window. As Don runs away, he looks back to see Alice pulled away from the window. He runs through a field and is chased by numerous infected, and several infected lurk on top of a hill and chase after him as well. Don makes it to the dock, where Jacob is already untying a boat. Don and Jacob get in, but an infected knocks Jacob out and into the water. Don tries to get him into the boat, but Jacob is submerged and blood pools around the boat. Jacob is infected and tries to attack Don, but he breaks free and cuts Jacob with the engine. Don makes it down the river and is full of remorse for leaving Alice.
Titles come up that outline the timeline from the outbreak of infection to the quarantine of Britain, to the arrival of American troops, to the last of the infected being killed, to the planning of repopulating, and finally 28 weeks later…
Scarlet (Rose Byrne), an American doctor, watches a single plane land at the airport. Among the people that have arrived is Tammy (Imogen Poots) and her little brother Andy (Mackintosh Muggleton). Scarlet is upset that it will take all day to process the civilians, and no one told her that they are now bringing in kids. Everyone undergoes several health inspections, and Scarlet notices that Andy’s eyes are different colors, a trait he inherited from his mother. She also makes a note that Andy is the youngest person in the country. After everyone passes the health examinations, the civilians are taken via subway to District 1, the designated safe zone that they will now live in. District 1 has twenty-four hour power, hot/cold water, a supermarket, and a pub. The district also has heavy American personnel stationed everywhere; their job is to protect the people. Snipers are placed on all the rooftops, and we are introduced to Doyle (Jeremy Renner), who passes the boredom by joking around with his fellow snipers and his friend Flynn (Harold Perrineau), a helicopter pilot. The civilians are strongly advised not to go outside of the safety zone, as the immediate areas are still not cleared. The subway arrives at the station, and Tammy & Andy are reunited with their father, Don. They embrace each other, happy that they’re together again. All of this happens as General Stone (Idris Elba) watches the civilians via cameras placed throughout the city. During this time Scarlet tells Stone that she’s upset about not being notified of children coming into the city, as they haven’t even prepared for minors yet. She’s afraid that the infection could come back, but Stone tells her that if it does they’ll execute Code Red which is the order to terminate all those infected.
The civilians for now will all be living inside a huge apartment building, until the American troops can deem houses fit for habitation and assign individual property to everyone. Don is the head janitor of District 1, and so has access to everything everywhere. He also lives in the penthouse of the apartment building, which makes the kids happy. As the family gets settled in, Don tells his kids that the apartment is temporary until they can get another home. He tells them that they can’t go back to their original home, since it’s outside of the safe zone (and he doubts he would want to go back there anyways). Andy asks what happened to their mother. Don makes his kids sit down and tells them what happened at the cottage, but he lies he says that there was nothing he could do for Alice, and she was killed by the infected. Don becomes tearful when he thinks about his cowardice and abandoning his wife. Later that night, Flynn listens to his headphones when Doyle pops out and scares him. Flynn gets after him for waking him from dreaming about his wife and kids. Before Doyle leaves, he gives him another scare and they laugh. He moves back to his position on the rooftop and looks into the apartment complex through the scope on his rifle. He sees a couple arguing, another couple having sex, Don and his kids playing in the bedroom, and a distressed Scarlet sitting by herself. In the middle of the night, Andy has a nightmare about Alice tearing off her face to reveal another one. He tells Tammy that he’s scared he’s going to forget what his mother looks like. Tammy assures him that he won’t, and the next day they plan to go back to their home to get photos and personal belongings.
In the morning, the kids sneak past soldiers on a bridge and run around outside of the safety zone while Doyle spots them. They run through the empty streets of London and stop when they see scooters in front of a pizza restaurant. Tammy goes inside to get the keys, and finds rotting food all over the place. She walks into the kitchen and finds the corpse of the delivery boy. She takes the keys and his helmet, giving it to Andy. They drive through the streets and pass abandoned cars. They make it to their home and go inside. Andy takes a picture of his mother and the kids pack their clothes into bags. When Andy goes outside and jumps on a trampoline, he sees someone in the attic. Thinking its Tammy, he goes upstairs and finds maggots on plates of rotting food. It’s a mess in the attic, and he sees someone cowering in the corner. Andy is shocked to find that it’s Alice, who’s alive after all. They embrace each other, but Alice hugs too hard and starts to hurt Andy. Tammy hears his screams, and Andy breaks free of his mother. The kids run outside to find soldiers in gas masks waiting for them while Flynn hovers above them. The soldiers find Alice and bring her back with them, forcibly washing her body before strapping her onto a stretcher. Scarlet examines her and notices that Alice’s left eye has blood in it. She sees that she has a bite mark on her arm, and takes a blood sample.
Don is called by the soldiers to a room where his children are being held. He’s upset that they went outside of the safety zone, but the kids are angry that he lied to them about Alice. Don can hardly believe that she’s alive. He leaves and sneaks through the facility, looking for his wife. Meanwhile, Scarlet tells Stone that Alice is infected with the Rage virus but she doesn’t have the same symptoms as the other infected. Instead of turning violent, she’s become a carrier for the virus. She can still infect others through saliva or blood, and Stone becomes convinced to execute her. Scarlet wants to do more work on her, but Stone tells her that she can continue her work on Alice’s corpse. Don eventually finds Alice and gains access to the room she’s in. She’s still strapped down, and he tearfully apologizes for leaving her behind. She says that she still loves him, and they kiss. Saliva gets into Don’s mouth, and he starts to violently become infected. He bleeds from his eyes, vomits blood everywhere, and bangs on the window. Don, fully infected, turns around and sees Alice strapped down. He beats her with his bare hands and bites her throat. Don then gruesomely shoves his thumbs through her eyes and smashes her head, killing her. He escapes from the room and goes on a killing frenzy, attacking every soldier he comes across. Stone sees the blood and dead soldiers. He executes Code Red and has the facility shut down.
Doyle and Flynn can’t believe that the order was given. The doors to the facility are locked and the power is shut down, switching to the back-up power. Stone goes to the command center and gives orders to his troops. The soldier watching Andy and Tammy tells them that everything’s alright, and leaves the room to find out what’s going on. While in the hallway, he’s attacked by an infected. The kids are locked in the room, waiting for the soldier to return. The infected soldier bursts into the room and pounds on the glass separating them. His head is blown off by Scarlet, who frees the kids and leads them through the facility. The troops won’t allow anyone to leave the building, and while Scarlet tries to convince them to allow the kids to leave Andy gets separated from them, being forced into the basement with all the other civilians. The soldiers lock the civilians in the basement, chaining the door shut to protect them from the infected. Andy, scared and alone, sits by himself near the back of the room. There’s another door near him, and he hears loud banging. Since the power was shut off, the only light is from people’s flashlights and lighters. Don bursts into the basement, and Andy sees that he’s infected. Don grabs a civilian and vomits blood onto him, and the infection quickly spreads throughout the basement while everyone panics in the dark. Andy manages to climb into an air vent and stays there as he hears people being killed and infected. The civilians break out of the room and run up the stairs, but are chased after by the infected. They make it outside, and Stone orders his men to only aim for the infected.
Doyle and the other snipers do their best and shoot the infected, but because everyone’s running it’s difficult to see who’s infected and who’s not. They can only tell when someone is attacked, and even then it’s too late for the victims. Realizing this, Stone orders the soldiers to kill everyone. The snipers and soldiers proceed to slaughter the civilians and the infected around them. Andy climbs out of the air vent and ends up right in the middle of the bloodbath. After shooting innocent people, Doyle can’t take anymore. He sees Andy through his scope and shoots an infected in the chest, splattering its blood on Andy’s chest. Andy runs to the supermarket, where several other people are hiding. Doyle leaves his position and goes after the boy. Andy walks through the darkened store and is startled by everyone he encounters. Luckily, he finds Tammy inside with Scarlet and is reunited with them. The survivors can’t believe that the soldiers are killing everybody, and Doyle shows up. He introduces himself to Scarlet, and they both ask each other why they aren’t at their posts. Knowing that everyone will be wiped out due to Code Red, Doyle volunteers to lead the survivors to safety. Doyle, Scarlet, Andy, Tammy, and a couple of others leave the store and enter the empty streets. Doyle tells everyone to stick together, and they run throughout the city while Andy gets a glimpse of Don following them.
Flynn calls Doyle and tells him to get out, because in four minutes they’re going to firebomb the city. They set up a rendezvous point, and the survivors are fired upon by a sniper. The sniper kills two or three people, and Scarlet is shot in the leg. Knowing the time limit they have, Doyle tells a survivor to run in a zigzag so that he can kill the sniper when he gives away his position. The survivor is too afraid to do it, and Andy runs out in the open. The sniper tries to shoot him, but Doyle shoots the sniper in the head. The remaining survivors run to a tunnel in the subway and brace themselves. The city is firebombed, filling the streets with explosions and fire. The infected are blown away, but Don manages to survive the attack. The explosions destroy the cameras set up around the city. The survivors run out of the subway station just before it explodes. As he sits down, Stone sees that the only camera still working is the one outside of the command center. And he sees several infected running straight for them. Elsewhere, the survivors make it across the bridge and wait at an abandoned carnival (the rendezvous). Scarlet tells Doyle that Alice had a genetic trait that caused her to be immune to Rage, and that it’s possible the trait has been passed on to the kids. Therefore, it’s imperative that the kids survive so that there’s a possibility for a cure.
Flynn flies to the location and is happy that Doyle is still alive. As the survivors wait for the helicopter, Doyle sees several infected lurking on the horizon. Flynn is angry that Doyle has people with him, and they argue about taking the other survivors. A man grabs onto the helicopter, trying to climb his way inside. Flynn tries to shake him off as the infected run towards the survivors. Flynn tips the nose down and cuts through the infected with the helicopter blades, cutting them into pieces and spraying the hanging man with gore. The man eventually loses his grip and falls. Doyle and Flynn set up another rendezvous point and Flynn flies away, but not before telling Doyle to ditch the survivors. Doyle, Scarlet, Andy, and Tammy run away as the infected are right behind them. Doyle shoots them with his rifle, but there’s too many. They run into a street but stop when they see that it’s filled with gas. Realizing that the soldiers are resorting to chemical weapons now, Doyle gets everybody inside a car. They cover all the vents and cover their mouths while the infected bang on the car, trying to get in. The gas quickly kills the infected around them, and Scarlet tries to start the car. Doyle sees soldiers walking towards them, wearing gas masks and setting the corpses on fire with flamethrowers. Scarlet can’t start the car, and Doyle realizes what he has to do. He tells Scarlet that he’ll meet them at the rendezvous point and gives her his sniper rifle. Doyle quickly exits and starts to push the car. The soldiers get closer and closer, but Scarlet finally is able to start the car. Doyle however is torched by his fellow soldiers and is burnt alive. Tammy and Andy watch in horror as Doyle dies behind them.
A helicopter shoots at the car as Scarlet drives through the streets, which are increasingly being filled with the gas. She winds up driving the car down into another subway station. This time there are absolutely no lights working there, so Scarlet leads the kids through the station using the night vision on Doyle’s sniper rifle. The kids are scared because they can’t see anything, but she helps them walk down the escalators and past the corpses around them. Tammy and Andy wind up falling down the escalator, and Scarlet frantically searches for them. She sees a glimpse of someone walking in the background. She finds Tammy, but can’t find Andy. While they search for him, Don shows up and beats Scarlet to death with the rifle. Don chases Andy down and bites his neck. Tammy picks up the rifle and shoots Don to death. Tammy breaks down and cries over the loss of her family. Turns out Andy’s still alive, but he runs off down a tunnel. Tammy tells him that they’ll always be together and runs after him. After a while, Andy collapses on the tracks. When he gets up, Tammy realizes that he’s not infected (though he has blood in his eye). Unbeknownst to her, Andy is also immune to Rage and has become a carrier for the virus. The kids make it to the rendezvous point, where Flynn holds them at gunpoint. After realizing that Doyle’s dead, he lets the kids fly with him. Flynn flies them to safety as they pass the burning ruins of District 1.
28 Days Later…In France, we see Flynn’s crashed helicopter in a field, but no bodies are shown. The film ends with the infected running towards the Eiffel Tower, the containment failing and the virus still spreading.