After surviving a car accident, Michelle (Mary Elizabeth Winstead) wakes up to find herself in an underground bunker with two men. Howard (John Goodman) tells her that a massive chemical attack has rendered the air unbreathable, and their only hope of survival is to remain inside. Despite the comforts of home, Howard's controlling and menacing nature makes Michelle want to escape. After taking matters into her own hands, the young woman finally discovers the truth about the outside world.