After a mysterious and brutal outbreak sweeps across the United States, a small family—a couple, Ray, Claire, and their young daughter Zoe—takes shelter in an abandoned fallout bunker just as the Air Force begins its bombardment of their town. With the outside world crumbling, the trio clings to a strict set of rules to keep fear at bay: stay calm, stay hidden, and never leave the shelter. The cramped space becomes a fragile sanctuary, and the family does their best to create small routines that give life some semblance of normalcy.
The quiet pressure inside the bunker starts to strain when supplies dwindle and a scavenger hunt for food becomes a grim reality. A rat intrudes into their dwindling ration supply, forcing them to confront an unsettling truth: the shelter is not as secure as it seems. They discover the rodent found another way in, slipping through an air duct rather than the main hatch. This realization shatters their confidence that the Breathers—shape-shifting threats that haunt the outside world—can be kept out. The family braces for danger while trying to reassure Zoe that they are truly alone.
Inside, the family’s hunger and fear push them to improvise. They kill the rat to stop its consumption of their food, but an accidental accident with a lamp starts a small fire. They manage to extinguish it, only to realize the smoke from the fire is escaping through the air duct, revealing their position to anyone nearby. The smoke leaves a spreading ash mark on the hatch, making their hideout even easier to detect. To survive, Claire and Ray sprint to the surface to cover the hatch and seal their location, while Zoe uses a homemade periscope to glimpse a distant humanoid figure—an alarming reminder that they are not alone. Against the rules, Zoe climbs through the barricade to warn her parents, and they retreat back into the shelter, though they’re soon pursued.
In a rapid flashback to the outbreak’s start, the family flees Kingsville on a highway, only to be stopped by a broad quarantine that the CDC enforces. The memory underscores how the world changed in an instant and how fragile their own chances of survival are. The current danger intensifies as more Breathers join the hunt and breach the hatch, forcing Claire, Ray, and Zoe back toward the surface. They manage a brief escape through the air duct, but Ray is captured and bloodied during the pursuit, and Zoe’s eyes reflect a terrifying transformation as she and her mother are forced to retreat once more.
Another flashback reveals the moment the town is bombed from the air. The family sprints toward a nearby shelter, and Claire sustains a rusty injury that turns suspiciously black as she examines it. They infer that the virus is airborne and that they have already contracted it, which reframes every later decision as a struggle against a foe that is both inside and outside them.
Back in the present, soldiers in night-vision gear arrive, test the survivors’ blood, and tighten the noose around them. Just as Claire and Zoe face execution, Ray appears and unleashes a storm of violence, killing several soldiers. He is shown with blackened veins and bloodshot eyes, and his strength seems superhuman as he fends off attackers before being shot multiple times. Claire and Zoe escape a net, and a furious Claire transforms along with Ray, slaughtering almost everyone in sight until a single wounded soldier remains. In a bitter turn, Zoe—still in a rage—nearly attacks Claire, but Claire calmly reminds her of the family’s rule to stay calm. With Ray dying, the two women sit at his side as the helicopter returns.
The trio slips away to a nearby sewer system, seeking safety in the dark. They are soon joined by another survivor, Joey, Zoe’s neighbor and friend, who guides them toward others who have also found shelter underground. As dawn breaks, Zoe notices that they have endured day 302 of the outbreak—a small miracle in a world where miracles are rare. Claire, ever-watchful, looks out toward the rising sun and into the window above the sewer, where the last trace of their former life lingers.
Not days. They are miracles, Ray had called each new dawn at the film’s start, and Claire’s final glance to the surface reinforces the chilling truth: they are no longer just survivors but a new, infected collective that will continue to endure, together, beneath the city.
