David Dutten is sheriff of Ogden Marsh, a picture-perfect American. But one night, one of them comes to a school baseball game with a loaded shotgun, ready to kill. Another man burns down his own house, after locking his wife and young son in a closet inside. Something is infecting the citizens of Ogden Marsh -- with insanity. In an effort to keep the madness contained, the government uses deadly force to close off all access and won't let anyone in or out -- even those uninfected. The few still sane find themselves trapped: Forced to band together, an ordinary night becomes a horrifying struggle for survival as they do their best to get out of town alive.