All her life, FBI special agent Mercy Kilpatrick followed the precepts of the preppers - a closed community preparing for the end of the world. But when a brutal serial killer appears in her hometown, these rules begin to work against her. 15 years ago, Mercy suddenly broke off relations with her family and fled the commune. It's time to go back and face your past. An elusive killer nicknamed the Caveman kills the survivors one by one. The locals' dislike of outsiders and the government makes Mercy an ideal agent. Together with police chief Truman Daley, they begin an investigation. The new partner sees that, having returned to his native land, the FBI special agent is nervous and hiding something. If everyone finds out what she did, it will ruin her career and possibly her life...