The film begins in the stunning Scottish Highlands, where a young boy named Jimmy is engrossed in watching “Teletubbies” alongside his sisters. Their peaceful moment is abruptly shattered when their mother rushes in, frantically trying to secure the children in a safe room as members of a horde infected with the Rage Virus break in and start their terrifying attack. While Jimmy manages to escape, his sisters are left behind in the chaos. He races to a nearby church, where his father, a priest played by Sandy Bachelor, is preparing himself for the inevitable doom that the Infected bring. Before Jimmy hides away, his father gives him a meaningful gift—a crucifix necklace to keep him safe. Tragically, the horde breaks through, and the priest accepts his fate, succumbing to the infection.
As the narrative unfolds, it is revealed through an onscreen text that the Rage Virus has ravaged the UK, leading to its quarantine from continental Europe; survivors now face the grim reality of a world where they must fend for themselves. Fast forward to 28 years later, and a community of survivors has established a settlement on Lindisfarne. Enter Jamie, played by Aaron Taylor-Johnson, who is imparting skills to his son Spike for his first hunt. Spike’s mother, Isla, portrayed by Jodie Comer, is ill and confined to bed rest.
The villagers rally around as Spike steps outside the community gates, preparing to kill his first Infected as part of a rite of passage. With his father by his side, they venture into the woods, where they encounter several overweight Infected. They successfully take down some of the creatures, with Jamie providing guidance and encouragement to Spike. As they explore further, they stumble upon a gruesome scene—an Infected individual tied upside down, which becomes a test of Spike's nerves as he waits for the right moment to strike. Finally, as the Infected breaks loose, Spike earns his kill.
However, as they progress toward the mainland, they spot a fire, which Jamie warns Spike to ignore. Encounters with a pack of infected creatures lead them into a tense chase, primarily driven by a formidable Alpha among the group. After strategically eliminating most of the threat, they hide until dusk before making their way back home. The tide makes their escape challenging, but they ultimately receive assistance from gatekeepers who fend off the Alpha just in time, celebrating their return to safety.
A celebratory gathering in Spike’s honor ensues, but a sense of betrayal arises when Spike witnesses Jamie engaging in an affair with another woman, shaking his trust in his father to the core. The impact of this moment leads Spike to directly question Jamie about the mysterious figure of Dr. Ian Kelson—a supposed madman who had once laid out bodies on the mainland. Jamie's cryptic silence during this inquiry culminates in a heated argument, resulting in a moment of violence that leaves both father and son in turmoil.
Determined to seek answers, Spike and Isla leave Lindisfarne in search of Kelson, despite Isla's declining health and unpredictable lucidity. Meanwhile, the mainland is chaotic, with NATO soldiers faced with the merciless Infected; only a handful survive to venture through a treacherous tunnel. As Spike and Isla navigate their perilous journey, they find temporary refuge in a gas station where a soldier named Erik joins their ranks. Together, they face another encounter with Infected, leading to a dramatic explosion that ignites tension and highlights their struggle.
Tragedy looms as Isla encounters an Infected woman, leading to a shocking birth and subsequent chaos. Erik and Spike fight for their lives as they navigate these harrowing encounters. In a fateful meet-up with Dr. Kelson, the complex layers of survival reveal themselves. Kelson introduces Spike and Isla to his ominous “Bone Temple,” a haunting monument built from the skulls of the deceased. He discovers Isla's terminal condition and offers her solace amid impending doom, showcasing the grim reality of their world.
With heavy hearts, Spike is separated from his mother after a heart-wrenching farewell, and he returns to Lindisfarne carrying a new burden. He brings back a baby—a survivor with no trace of the Rage Virus—named Isla, perfect for the new beginning they hope for. Jamie desperately searches for his son on the turbulent river, only to find emptiness.
Finally, the story takes a twist as 28 days pass. Spike, now faced with the mingling threat of the Infected once more, encounters a mysterious blonde man, Jimmy, who offers friendship amidst the chaos. This encounter suggests not only survival but also the rebirth of trust and camaraderie in a shattered world. As they join forces, this chapter in their lives becomes interwoven with themes of hope and resilience.