Based on the novel of the same name by Larry Watson, "Let Him Go" centers on retired sheriff George Blackledge (Kevin Costner) and his wife Margaret (Diane Lane) who, following the loss of their son, leave their Montana ranch to rescue their young grandson from the clutches of a dangerous family living off the grid in the Dakotas, headed by matriarch Blanche Weboy. When they discover the Weboys have no intention of letting the child go, George and Margaret are left with no choice but to fight for their family.