In 2012, the world succumbs to a catastrophic viral pandemic that transforms individuals into feral creatures overcome by rage. Amidst this turmoil, a young girl named Abigail prepares to evacuate with her family — her mother, played by Caroline Boulton, and her brother — to join their father, who is abroad. However, just as they are about to leave, a feral attacks their home, resulting in her mother and brother becoming infected and turning into ferals themselves. In a stroke of fate, Abigail is rescued by Cassius, a police officer, and they retreat into the wild, where they learn to survive by hunting and scavenging, moving their camp regularly to evade the ever-present ferals.
Fast forward ten years later, and both Abigail and Cassius devise a plan to escape to an island off the eastern coast of the United States. Their hopes are soon dashed when a pack of ferals encroaches on their camp. In the chaos that ensues, they encounter a group of armed survivors, but the situation turns dire as most of them are slaughtered during a feral attack. Abigail and Cassius manage to flee with a heavily pregnant woman named Megan and her husband David. The violent encounter comes with a heavy price; Cassius unknowingly ignites the wrath of the feral pack's alpha by killing its mate.
With their vehicle out of commission, the group finds solace for one night in an abandoned city where Abigail's father had stashed a private turboprop plane. During their stay, Abigail learns from Megan and David that they intended to reach a boat town in the Northeast, which they have managed to contact via radio. Abigail feels compelled to join them, but due to Cassius' deep bitterness and loss of friends and loved ones throughout the ordeal, he decides to stick to his initial plan.
As dawn breaks, the feral pack picks up their trail, forcing the group to hastily move on to the airport. They locate the plane but face continued assaults from the relentless pack before they can complete the necessary repairs. In a mad dash, they manage to escape, only to find themselves crashing shortly after takeoff due to the engine's failure. Faced with yet another setback, Cassius decides they must head to the boat colony that is closer.
As night descends, they reach a forest hut owned by Norton, an engineer who offers them shelter. However, their respite is short-lived, with Norton positing that the pandemic serves as nature's way of purging the weak from humanity. The group is soon incapacitated by drugged drinks he serves them, and as David's infection deteriorates, Norton imprisons them and uses a sonic gauntlet to release his feral wife upon them. In a pivotal moment, David fights her off, allowing the group to escape in a rover.
The stress of their travel prompts Megan to go into labor, but a blockage on the road forces them to proceed on foot. In a moment of bravery, David stays behind to confront the ferals, sacrificing himself as the Alpha brutally kills him. Eventually, Abigail, Cassius, and Megan arrive at King's Harbor, a refuge made up of freight ships encircling a dilapidated dam project. Here, Megan gives birth to a daughter but tragically succumbs to complications during childbirth, leaving Cassius to promise that he will care for her baby.
In the midst of their new reality, Abigail forges a friendship with a local youth named Roderick, who teaches her about an explosive booby trap and an escape tunnel they can use if the ferals invade their safe haven. The following events take a dark turn as Norton tracks them down to the colony, unleashing ferals on the unsuspecting colonists. Working together, Abigail and Cassius organize an evacuation, but Norton’s relentless pursuit leads to a climactic confrontation where Cassius dismantles Norton's protection. Ultimately, the ferals ensue, leading to Norton's demise.
In a shocking twist, Abigail encounters the Alpha, who reveals himself as her father. In a moment of courage, she and Cassius escape through the tunnel just before Roderick detonates explosives that obliterate the colony and the ferals within. Rejoining the remaining colonists, they face one final battle against the Alpha. After an intense showdown, Abigail overcomes her fear and takes down the formidable creature. With the colony destroyed, Abigail and Cassius turn their eyes toward the horizon, embracing their original plan as they lead the survivors toward their promised island sanctuary.
