Due to a leak from a secret factory making biological weapons in Craigavon, a virus was released that initially affected the workers in the plant but was spread on the wind to the surrounding region.
Within a short period, anyone who contracted the zombie virus died. Then the dead began to reappear and cases began to be documented on social media. Reports spread rapidly of relatives returning as zombies: difficult-to-kill, flesh-eating, shells of their former selves. They displayed an insatiable appetite for human flesh and a resistance to injury. Medical staff, the police and eventually the military seemed unable to contain them. Only by destroying the brain could they be stopped.
By the time this was discovered it was too late: there was widespread transmission across the east and south of Northern Ireland as people contracted the virus after being bitten by zombies or by breathing it in. Communities were devastated by zombie attacks; panic meant the breakdown of all semblance of normal life. There is no longer a functioning government, health service, or transport system, and supplies of food and water are running low. Refugees have started making their way towards the north-west, hoping to stay safe or get evacuated: some of them unwittingly bringing the virus with them.
Locals have formed themselves into a Zombie Resistance Force, centred on the Magee Campus, as a place of refuge and a centre from which evacuations are being coordinated, via boats on the River Foyle. New arrivals are monitored for any signs of the virus, before being trained to keep themselves safe against zombie attack.