When Cabot Howard's ex-wife, Leana, flees the pandemic with their son Porter to the backwoods town of Rookfield, Cabot sets off after them. Once he arrives, however, he finds Leana is in hiding, her family won't hand Porter over, and the townsfolk are deadly serious about always wearing masks. The town's children dress like little plague doctors and the adults are hellbent on getting Cabot out by nightfall.

Despite being alone and under attack, Cabot won't leave without his son. Nothing-not ex-in-laws, not the sheriff, not even whatever monstrosity might be lurking in the woods just behind the barn-will stop Cabot from getting them out of ... Rookfield.