David Dutton (Timothy Olyphant) is the sheriff of Ogden Marsh law abiding citizens. But one night, one of the comes to a school baseball game with a loaded shotgun, ready to kill. another man burns down his own house, after locking he's wife and young son in a closet inside. Something is infecting the citizens of Ogden Marsh...with insanity.
The few still sane find themselves trapped: Sheriff Dutton; his pregnant wife, Judy; Becca, an assistant at the medical center; and Russell, Dutton's deputy and right hand man. They are forced to band together, on an ordinary night becomes a horrifying struggle for survival as they do their best to get out of town alive.