Plot
After an argument with her fiancé, a young woman named Michelle leaves her New Orleans apartment. That night, while driving through rural Louisiana, she hears news reports of blackouts in several major cities. Suddenly, her car is struck off the road, knocking her unconscious. Awakening with an injured leg, Michelle finds that she is chained in a bunker. Her captor, an older man named Howard, unchains her. He explains that he took her to the bunker to save her life and claims that the air outside is poisoned after an attack.
Howard gives Michelle a tour of his bunker, introducing her to Emmett, his construction assistant. Through a viewport at the airlock, Howard shows her two decayed pigs outside, supposedly killed in the attack. Michelle also sees Howard's truck and recalls it striking her car. She privately talks to Emmett, who assures her that the attack is real: he begged to be let in after witnessing the attack.
During dinner, Howard shows flashes of jealousy when Michelle grows closer to Emmett. Michelle steals Howard's keychain and flees. At the airlock, she prepares to open the outside door when she witnesses a woman covered with lesions screaming to be let in before dying. Michelle retreats to the bunker, and Howard explains that he accidentally struck her car while rushing to the bunker. Michelle is seemingly convinced.
Over the next few days, the trio begins to adapt to life underground, and Howard opens up about his daughter, showing Michelle a photo. After something loud passes overhead, the air ventilation system fails. Howard sends Michelle through a small duct to reactivate it. In the control room, she finds a padlocked skylight with the word "HELP" scratched on the inside, and an earring she saw in the photo. Michelle shares this with Emmett, who recognizes the girl as a local who disappeared two years earlier; Howard's actual daughter left with his wife. Deciding to escape, Michelle fashions a makeshift hazmat suit by stealing Howard's supplies and tools.
Howard discovers their plot and threatens to immerse them both in perchloric acid. When Emmett claims responsibility, Howard shoots and kills him. He tells a shocked Michelle that now they can be a family of two. While Howard cleans up, Michelle secretly finishes the suit. When discovered, Michelle flees, overturning a barrel of acid. The corrosive puddle disfigures Howard and starts a fire. Leaving Howard to his fate, Michelle dons the suit and escapes.
Outside, Michelle sees an approaching biomechanical alien craft, attracted by the bunker fire. It drops a Human Scale Parasite that investigates the car alarm and tries unsuccessfully to get at Michelle. The craft discharges a green gas, which she protects herself from by wearing her mask, and takes shelter in Howard's truck. The craft's tentacles lift the truck to get to Michelle, but she destroys it with a Molotov cocktail. She drives away in the dead woman's car.
On the car radio, Michelle hears an emergency broadcast about successes in the battle with the invaders. It mentions that a safe zone has been set up in Baton Rouge, but when she arrives at a crossroads, she heads for Houston, where help is requested from people with medical or combat training. Two approaching massive alien craft are revealed in the lightning of the distant stormy sky.
