"We are headed for the green-zone, our area of security and reconstruction, designated as District One. District One is located on the Isle of Dogs. Although the Isle of Dogs is completely safe, the surrounding area of London is not....."
— DLR Soldier
As implied by the title, the story of 28 Weeks Later — the sequel to the 2002 horror film 28 Days Later — begins twenty-eight weeks after the events of the first film, where a literal hate plague ravaged Britain: a U.S.-led NATO force has established a foothold in the Isle of Dogs, where it's started the process of repatriating the countless British citizens left stranded after leaving their country during the Rage virus outbreak. Those who return end up quarantined in "District One" under heavy surveillance by US soldiers; Don Harris (played by Robert Carlyle), one of the quarantined, became one of the few people trapped in London who managed to survive the outbreak. Haunted by the memory of being forced to abandon his wife during an attack by a horde of infected Rage carriers, Don ends up reunited with his two children, Tammy and Andy, when they become new residents of District One.Since the Infected starved to death weeks ago and no evidence suggests the plague crossed over into other species, the survivors begin the process of trying to rebuild their former lives while the NATO forces begin an extensive effort to clean up further areas of London to prepare for rehabitation. When Tammy and Andy sneak out of District 1 in order to visit their former home, however, the survivors — and the soldiers protecting them — soon discover lingering traces of the Rage virus, which kicks off a frantic fight to keep the plague from spreading once more.
28 Weeks Later provides examples of the following tropes:
After the End: The premise of the sequel involved attempts by the U.S. military to recolonize Britain after all the Infected were apparently cleared out.
Air-Vent Passageway: Andy uses one to escape a locked room after the infection spreads amongst the crowded civilians in District 1. Justified in that Andy is small enough to fit inside an air duct.
America Saves the Day: Inverted. While initially having things under control, by the end of the film the infection has broken out and the U.S. military fails to contain it. The catastrophe could've been averted if they just had more guards posted on watch.
It should be noted that ultimately, the Harris family was responsible for the outbreak; Tammy and Andy only had to follow orders and not go outside the district, and Alice might not have been infected in the first place if Don had saved her. Or just not kiss her while in quarantine.
It can also be said that if Doyle, Flynn, and Scarlet had followed orders then then the virus would not have escaped to Europe with Andy as the carrier.
Apathetic Citizens: They've all just survived a viral outbreak. One assumes that even the ones who were outside of the UK and returned had been shown videos and been told how virulent the Infected were before they even returned. Yet when they are herded to a secure location for their own safety - no matter how unsafe that actually turned out to be in the end - they bicker and complain to the troops about it.
Artistic License - Gun Safety: Snipers are shown passing time by using the scopes attached to their rifles, rather than binoculars, to spy on residents of the district.
Black Dude Dies First: Averted — Flynn survives all the way to the end of the movie, though he probably dies afterward along with everyone else.
Blind Alley: Seen in one of the short films made for 28 Weeks Later. A man is pressed up against a wall as the Rage virus infected run past the alley — presumably their blinding anger prevents them from doing common sense things like looking around for someone who's gone out of sight.
Chekhov's Gun: Heterochromia. Genre Savvy tropers can pick out the entire plot of the movie simply from one conversation in the first few minutes.
Daylight Horror: The beginning sequence and the final image of the movie, particularly.
Death by Pragmatism: Inverted. When the quarantined civilians inside Sector One initially break out, chased by/mixed with Infected, the U.S. soldiers are ordered to only fire on infected. This causes their lines to be swamped by panicking civilians and infected that weren't identified fast enough. Since the crowd of civilians and infected were coming out of one large set of doors, with multiple automatic weapons trained on it, if the soldiers had unloaded immediately on everyone coming through, they might have been able to stop the infection right there.
Downer Ending: London has been decimated once again by the virus and the subsequent firebombing, all of the thousands of London settlers have been horribly killed, and the Infected have overrun France, meaning they'll probably spread to much of the Continent. The children's fate is left up in the air. It's possible they survived, but it's also implied that the plague spread to the mainland via Andy.
Eye Scream: This sequel plays this trope horrifyingly straight. After reuniting with his wife, Don gets infected by the virus and kills Alice by gouging her eyes out. This is a direct comparison to the first movie's hero, who does the same to a soldier without being infected.
Although she might have rather died from him beating the shit out of her first and then ripping her trachea off by biting.
Harbinger of Impending Doom: When a frantic child is allowed into the barricaded home that Don, Alice, and a group of other survivors are holed up in just weeks after the infection began, his arrival portends the events to come.
Child: "My mum, my dad... They're trying to kill me. There's others too."
Don: "How many others?"
Child: "... Loads."
Fake American: Australian Rose Byrne and, somewhat oddly, Briton Idris Elba as American soldiers.
False Reassurance: "Everything's fine, I'll be back in a moment." The soldier does return in a moment, but as an infected.
Heroic Sacrifice: Doyle pushes off the others to safety before getting torched by one of the extermination squads. Possibly foreshadowed with this line:
"Their [Tammy's and Andy's] lives are far more valuable than mine...or yours."
The people in the basement when an infected Don bursts in. Even though everyone's screaming and panicking, they have enough semblance to recognize Andy as a child, lift him up over their heads and crowd-surf him over the carnage, and then shove him into a ventilation shaft knowing only he would fit in.
Idiot Ball: Quite apart from the above example, if either the Chief Medical Officer or Sgt. Doyle had bothered to explain why the children were so important, even to the children, someone might have been more careful and we might just have avoided the infection of France and the breach of the sea border which was holding back the infection.
The lack of the most basic security measures in District One. No effective barrier on bridges and few guards. It's about as easy as sneaking out of high school grounds during lunch break.
Easier, actually - have you seen the security in American schools these days?
In the beginning of the outbreak, the civilians are herded into a containment area, and the doors are locked and chained shut. Well - one of the doors...
The fact that that was even the security protocol. We are shown earlier that everyone has their own reinforce-able apartment cells. It would have made a thousand times more sense for them to all be sent back to their rooms with guards manning the hallways.
On the children's part, they decided to sneak out of District One even after the military told them explicitly not to do so and why. As poor as the security is on the military's part, they may not have been expecting someone to do something as stupid as what Tammy and Andy did.
If the military had placed even one guard on a woman they had every reason to believe was an asymptomatic infected, or ordered one placed on her immediately after they confirmed this, all would have been well.
Don holds the biggest one of all. He pretty much single-handedly caused the second outbreak.
It Can Think: The Infected in this movie seem to have a bit more going on upstairs than the ones in 28 Days Later, particularly Don who not only manages to survive the firebombing of District 1, but tracks his children through London all the way to the Underground. He also uses a gun as a blunt weapon when he kills Major Scarlett. He's not the only Infected to survive District 1, either, which implies he's not the only one who's retained some measure of intelligent reasoning.
All There in the Manual. A line in 28 Days Later: The Aftermath indicates that while the Rage virus causes the higher brain functions to atrophy after a few days, victims still retain a lot of their reasoning skills until then. Presumably as recent infectees, Don and the others in 28 Weeks Later hadn't yet reached that stage.
Love Hurts: And how. An estranged couple, each thinking the other dead, reunites and is happy that they're both alive and well... and kiss, starting the plague anew (and directly leading to the Eye Scream mentioned above).
Room Full of Zombies: One of the infected creates this by getting into a room of normal people during a lockdown.
Scylla and Charybdis: As Code Red was being executed, a survivor in a warehouse remarked, "We take one step out that door, if the infected don't get us, the snipers will."
Later, Major Scarlett was forced to navigate through a dark, dangerous subway to prevent being killed by Apache helicopters patrolling the poison gas-filled streets. This results in an infected Don ambushing and beating her to death when she was searching for Andy. The children were able to make it to safety.
Shoot Everything That Moves: There's a fairly horrific scene where the soldiers are attempting to secure a compound by shooting infected, except that due to the speed and the confusion it's hard for them to make out just the infected. Then the snipers get the order that everyone is considered a target...
This Loser Is You: Within the first ten minutes of the film, during the welcome back speech, the woman says "As you can see, District 1 is currently under the protection of the U.S. Army." This may have been replaced with "Look around. You're screwed.", which is clearly proven in the next ten minutes.
Too Dumb to Live: The Virus wiped out the entire population of Britain in under a month, but apparently despite the fact that the Virus was only contained due Britain being an island, the U.S. Military deemed a mere six months to be enough time to adequately classify it as safe. Realistically, Britain would have been kept under a UN Quarantine for decades if not centuries to eliminate any lingering trace of The Virus before any attempt at recolonisation began.
Despite its virulence, the disease was limited to infection by contact with bodily fluids, heavily limiting the risk under proper safety precautions. This combined with the pressure of the massive refugee population would have pushed the recolonization forward despite the risks. The Idiot Ball is grabbed only when it's made apparent just how poor the security measures actually are, failing even at the most mundane level.
There are multiple instances throughout this movie where the second outbreak would have been easily prevented if only the US military had decided to post guards everywhere, leading to a situation where instead of being crazy, the guards don't appear to even exist! The lack of security both internal and external, leads to two children being able to easily escape the safe-zone and let the Rage Virus escape quarantine once again.
Any quarantine room would have had doors that might have allowed entry with a keycard, but exit only with approval from someone outside the room. This simple precaution would have locked Robert in with his carrier wife, and the death toll would have been two. Similarly, if the civilian quarantine cells had been secured at all, the infection would never have reached the thousands of people trapped in there.
The little kid from the prologue, who didn't try to lose the infected pursuing him before knocking on the first door he saw, then when the infected naturally burst through the door, decided to run away instead of staying with the others.
Typhoid Mary: Alice is an asymptomatic Rage carrier, and it's implied at the end that Andy may have become one as well.
Villain Has a Point: Despite the moral grey area in what they do, the US military's ultimate goal is to prevent the virus from spreading to the rest of the world, which could bring about the end of humanity. And if the US government had succeeded in killing the survivors, Andy would never have brought the Rage virus across the English channel and presumably infected France.