Princess Bertha of Paris is shocked to learn of her impending marriage to the heathen king of Kent. But their barbaric world is dramatically changed by the coming of Augustine from Rome, on a mission to impress his hero, Pope Gregory the Great. As the new arrivals face hostility and murder, the powerful king sees a way of using Augustine to further his ambition. However, Bertha's eldest son is in league with the banished priests and she knows her husband's vengeance will be terrifying should he find out ... In this Anglo-Saxon world on the threshold between pagan beliefs and Christianity, the feisty Bertha and the timorous Augustine form an unlikely alliance.