In the heart of East London's dynamic construction scene, two laborers inadvertently uncover an ancient catacomb, sealed for centuries by royal decree during the reign of Charles II. Instead of informing the authorities, they recklessly delve deeper, driven by the allure of treasure, but awaken an undead curse that arises from the depths of the ruins. As chaos begins to engulf the area, a different story unfolds involving the MacGuire brothers.
Terry MacGuire and his younger brother Andy devise a bold plan to rescue their grandfather Ray's retirement home from impending demolition. They rally their cousin Katy, the hapless Davey Tuppence, and Mickey, an Iraq War veteran with a fragile psyche and a metal plate in his forehead. As they execute their bank heist, expecting to nab a modest sum, they inadvertently stumble upon a massive £2.5 million, mistaking them for representatives of Hartman Construction due to the bank manager's blunder. Yet, as they scramble to escape, Mickey takes charge, forcefully rounding up bank employees Emma and Clive for their getaway.
However, upon their attempt to exit, a menacing group of reanimated corpses descends upon them, a consequence of the very outbreak plaguing the East End. Meanwhile, at Ray's retirement home, the undead epidemic starts to wreak havoc among the residents. Amidst the bedlam, Ray and his fellow retirees, including Peggy, former gangster Daryl, and Eric, find refuge in the kitchen, hoping for rescue. Ray takes a moment to save Hamish, ensuring his safety along the way.
As the MacGuire siblings, Katy, Mickey, their hostages, and their newfound fortune travel through the devastated streets, they reach a designated safe house. Tragedy strikes when Mickey, having been bitten by a zombie, becomes increasingly erratic. As they tune into a radio broadcast covering the chaotic events, the true scale of the outbreak dawns on them, casting a shadow of uncertainty over their plans. Emma pleads for her release, arguing that their mission is misguided, while Katy defends their actions, insisting they aim not for selfish gain but to preserve Ray's retirement home.
Tensions rise when Mickey, frustrated with his group, isolates Emma and Clive, intensifying his menacing grip over them. But destiny plays a cruel trick; Mickey’s earlier bite begins to take its toll, weakening him as Terry seizes the moment, forcing a grenade down Mickey’s throat to end his spree of terror. Amidst the uproar, Clive irrationally grabs Mickey's gun, suggesting they surrender, only to face a gruesome fate at the jaws of lurking zombies—a miscalculated decision that also seals Davey’s doom.
With their numbers dwindled and spirits crushed, the group hastily loads their spoils into Terry's vehicle, strategizing their next move towards Ray's retirement home. Their search for Emma’s younger sibling leads them to a haunting discovery—her sister in a state of undead stasis. Emma’s hope for a cure prompts them to spare her sister, and they fortify themselves with Mickey's cache of weapons.
Upon their arrival, they embark on a daring rescue mission to break the undead siege, successfully freeing Ray and the remaining residents. In a surprising twist, they commandeer an iconic red London double-decker bus, but mechanical malfunctions soon halt their escape. As they quickly venture to find a boat, they find themselves thwarted by missing keys and a boat chained to the dock.
In a moment of sheer selflessness, Ray sacrifices his safety for the group's, but miraculously, he survives and joins them as they finally make a desperate escape down the river. As they drift toward an uncertain future, their determination to reclaim East London from the clutches of the undead shines through, inspired by Ray's defiant proclamation that they can conquer the chaos besieging their home.
