While on a fishing trip, Harry Baldwin (Ray Milland) and his family hear an explosion and realize that Los Angeles has been leveled by a nuclear attack. Looters and killers are everywhere. Escaping to the hills with his family, he sets about the business of surviving in a world where, he knows, the old ideals of humanity will be first casualties. Not one to give up, he holds up a store for supplies and hides the family in a cave.

Christmas 1183--an aging and conniving King Henry II plans a reunion where he hopes to name his successor. He summons the following people for the holiday: his scheming but imprisoned wife, Queen Eleanor of Aquitaine; his mistress, Princess Alais, whom he wishes to marry; his three sons (Richard, Geoffrey, and John), all of whom desire the throne; and the young but crafty King Philip of France (who is also Alais' brother). With the fate of Henry's empire at stake, everybody engages in their own brand of deception and treachery to stake their claim.