A young woman, strong, quiet, a bit of a loner with a haunting past, struggles through the day to day existence of living in Brentwood, the glamorous town in Essex that's full of fake people, spray tans and flashy cars. Luckily for her, overnight a catastrophic event occurs across England. Something is infecting and killing people in the millions. Then those murdered victims rise up and go on to kill more. Whatever is causing it is spreading too fast for the authorities to contain and, within a few hours, the government infrastructure has collapsed. Martial Law has been implemented and the British Isles have been blockaded.
England has been left to die.
Wandering into a deserted and blood soaked Brentwood the next morning, the young woman, Riley, soon encounters another survivor. He's a cocky young guy, friendly but with an air of street smarts and menace about him. Before she can figure out what is happening, they pair are set upon by thousands of infected people, all charging down the street after them. They escape and retreat to a secure storage warehouse, where other survivors are waiting for them. Amongst the survivors is a cop, a student, a shop manager, a footballer's wife, a fat bloke and a soldier, Ahern.
Ahern is trying his best to keep control of the situation but, due to being totally cut off from his chain of command, he's starting to unravel.
Riley learns that whatever has happened has consumed the whole of Britain. Ahern tells her that the military has retreated to the safety of the sea and is conducting rescue services around and near the coastal cities. Riley persuades the group, and a reluctant Ahern, to head for Southend On Sea, only 30 miles away from Brentwood, as it would be the most likely point of rescue for their part of Essex.
After being attacked by an infected horde, the survivors take refuge in a local nightclub and barricade themselves in. They discover another survivor hiding in there. She tells them of how the town fell the night before, of how people were being killed in the thousands across the area and of how the authorities appeared to abandon the populace. This prompts the other survivors to swap their own tales of the events of the previous 24 hours. They learn from Ahern that the military detonated two high altitude nuclear bombs, with the resulting EMP blast knocking out everything electrical and mechanical, in a last-ditch effort to halt the spread of the infection.
The group of survivors, now much fewer, set out on their trek the next morning. They travel cross-country, utilising tunnels and footpaths, to get to Basildon, the halfway point on their journey. They take refuge in a barn for the night and, over some scavenged food and a few beers, finally start to bond and come together as a cohesive unit.
The next day, the group head for the coast. Tragedy strikes along the way but, eventually, they arrive in Southend. The city appears deserted at first but then they hear a familiar sound: Southend isn't deserted.