Doomsday

In 2008, an unknown killer virus, known as the "Reaper virus", has infected the country of Scotland, turning its entire population into savage animals with symptoms of loss of emotion control and emotional outbursts. Unable to contain the outbreak or cure the infected, the British government builds a massive 30-foot wall that isolated Scotland from the rest of Great Britain. Whilst the quarantine was deemed a success, the extreme method employed by the government destroys diplomatic and economic relations between the UK and the rest of the world. Now a pariah state, the UK collapses into a dystopia, rife with unemployment, civil unrest and extreme economic turmoil.

Twenty-seven years after the start of the quarantine, a group of armed police officers discover several people in London infected with Reaper virus during a routine investigation. Prime Minister John Hatcher shares satellite footage of survivors in Scotland with domestic security chief Captain Nelson. Believing a cure may exist, Hatcher orders Nelson to send a team into Scotland to find medical researcher Dr. Kane who was working on a cure when Scotland was quarantined. Nelson chooses his top police officer, Major Eden Sinclair, to lead the team. Sinclair is originally from Scotland, having escaped as the quarantine began at the cost of her right eye. For Sinclair the mission is also personal, as she hopes to learn if her mother survived or not.

Sinclair's team crosses the wall to Glasgow, Dr. Kane's last known location. In Glasgow, while searching the local hospital for survivors, Sinclair and her team are ambushed by a group of marauders. Sgt. Norton and Dr. Stirling manage to escape, while the team suffers heavy casualties. Sinclair and Dr. Talbot are captured by what turns out to be a huge gang of brutal cannibals, led by the power-hungry Sol, who plans to use her as leverage to cross the wall, allowing his army to start their invasion on England, which will bring Great Britain into the Golden Age. He then leaves for the sacrificial ceremony to join the rest of his gang, who burn Dr. Talbot alive before devouring his body. With the help of Cally, another prisoner, Sinclair escapes and kills Viper, Sol's second-in-command. She meets with Norton and Stirling, and the three escape on a train. Cally reveals that she and Sol are Kane's children. Unsatisfied with Kane's rule, Sol abolishes martial law by creating his own army.

Meanwhile, back in London, everyone infected with the virus riots, destroying everything in sight. Hatcher plans secretly to isolate the central London area because of the infection when an infected man breaks into Hatcher's office and tries to kill him. Nelson shoots and kills the infected man, but his blood splatters on Hatcher. Hatcher is quarantined by his right-hand man, Michael Canaris, who also takes his place as de facto prime minister. Hatcher later commits suicide, knowing that his exposure means an almost-certain death sentence from the virus.

After leaving the train, Sinclair's group is arrested by soldiers armed with archaic weapons and armour. They are taken to a medieval castle and imprisoned. Their leader, Marcus Kane, tells Sinclair the truth: there is no cure, only people with a natural immunity, which was the reason why Scotland was placed under permanent lockdown. Originally a medical researcher, he was devastated when his family was left behind during the quarantine. After losing his wife, Kane became a twisted, sadistic lord who now hides from the world around him. Angry to see Sinclair return to Scotland after the start of the quarantine, Kane sentences her and her group to death, pitting Sinclair against Telamon, his executioner, in a small fighting ground to entertain his followers. During the duel, Sinclair subdues and kills Telamon while the rest of the group escapes, retrieving their equipment and rescuing Sinclair.

Sinclair, Norton, Stirling and Cally escape to a fallout shelter entrance on horseback. They locate an underground facility in the forest and find an intact 2007 Bentley Continental GT, which they fuel up. Kane's medieval knights arrive and kill Norton. Sinclair and the others drive the Bentley back to the quarantine wall. On the way, they are intercepted by Sol's gang, which seeks to avenge Viper once and for all. After a high-speed chase, Sol and many of his men are killed and Sinclair's group escape.

Using a phone retrieved from the fallout shelter, Sinclair calls Canaris, who later arrives in a government gunship. Canaris then tricks Sinclair into trading Cally (after Stirling originally suggests that her blood can be used to create a vaccine to treat the virus), revealing himself as the creator of the Reaper virus, which is, in fact, a bioweapon that can spread all over the UK as both a form of population control and shady profit; Canaris says that he intends to use the virus to wipe out a majority of the UK's population and later lead the survivors into a new world under his reign.

Cally and Stirling board the gunship with Canaris while Sinclair returns to her old house in search of her mother, followed by Nelson, who flew into the quarantine zone to speak with her. While Sinclair finds out her mother died in despair during the quarantine, she is able to retrieve a picture of her. Sinclair gives Nelson a recording of Canaris' genocidal scheme. The recording is later broadcast to the rest of the country, much to Canaris' dismay, as it spells doom to his career and sub-sequential criminal conviction. Sinclair retrieves Sol's head and returns to his gang; she throws the head onto the ground, announcing to the marauders, “If you're hungry, try a piece of your friend”. The marauders stand in shock for a moment before bursting into cheering, accepting Sinclair as their new leader.