Shaun is a disengaged electronics store employee with little ambition and a mundane life in London. Stuck in a rut, he’s unable to muster the energy to make any significant changes in his life. Shaun is not only failing at his job, but he’s also disappointing his long-suffering girlfriend, Liz, who wishes Shaun would move on from his immature days, primarily characterized by constant pub visits with his crude best friend, Ed. Liz, fed up with Shaun's lack of direction and Ed's influence on him, ultimately gives Shaun an ultimatum to grow up. Shaun decides to turn his life around, promising to make more of an effort in their relationship.

As Shaun embarks on his new path to self-improvement, he's unaware of a mysterious virus that’s spreading across London, turning the population into zombies. Initially oblivious to the chaos unfolding around them, Shaun and Ed soon notice the strange behavior of people on the streets. After a peculiar encounter with what they think are just drunk individuals, the gravity of the situation starts to dawn on them. Understanding the threat, Shaun hatches a plan to salvage his relationships and protect his loved ones. He aims to reconcile with Liz and save her and her flatmates, as well as his mother and step-father, by seeking refuge in the one place he knows best – their favorite local pub, The Winchester.