The narrative unfolds as Michelle abruptly packs her bags and flees her fiancé, desperately
trying to escape her turbulent relationship. While driving at night, listening to a frantic news broadcast about widespread electrical blackouts, a massive pickup truck violently rams her vehicle off the road.Michelle regains consciousness chained to a wall in a concrete bunker. Howard, a paranoid survivalist and former
military contractor, tends to her injuries. He explains that an apocalyptic chemical or nuclear attack has devastated the surface world, rendering the atmosphere toxic and humanity nearly extinct. Alongside Howard is Emmett, a local young man who claims he helped build the bunker after believing Howard's frantic warnings.Initially, Michelle views herself as a captive and plots her escape. She manages to break free from her room and reaches the airlock, where she encounters a hideously disfigured woman begging to be let inside, frantically clawing at the glass and screaming about monsters. Howard drags Michelle away, insisting the woman is infected by the outside air. Convinced Howard is a deranged kidnapper who murdered the woman outside, Michelle focuses entirely on constructing a makeshift hazmat suit from household items to break out.As days pass, the trio develops a bizarre domestic routine filled with tense board games and shared meals. Emmett confesses he lost his ticket to the bunker to Howard, realizing the dark reality of their situation. However, tension skyrockets when Michelle discovers a pair of blood-stained earrings belonging to Brittany, a missing local girl Howard claimed was his niece. This chilling discovery confirms Brittany was not safe elsewhere as Howard had lied; she was murdered inside the facility.Armed with homemade weapons, Michelle and Emmett plan to overpower Howard and escape. Just as they finalize their plan, Howard discovers their preparations, leading to a violent confrontation where he murders Emmett with acid. Michelle narrowly escapes into the ventilation shafts, finally finishing her makeshift suit and breaking through the heavy exterior door.Stepping outside into the misty Louisiana countryside, Michelle expects certain death. Instead, she breathes the air and realizes the atmosphere is completely breathable. Her relief is short-lived as a massive, organic alien spacecraft descends from the clouds, pursuing her and dropping terrifying extraterrestrial predators. Trapped in a barn, Michelle uses a Molotov cocktail to destroy an alien ship. Looking up at the sky, she sees a distress signal on the radio for survivors in Baton Rouge. Refusing to succumb to despair, Michelle changes direction, driving toward the city to join the human resistance, ready to fight for a future against the colossal invasion.