The nine witch queens of Ys have cast spells to lure an able leader to their city—someone who will replace the hated Colconor as king of the city and who will make a good leader. The city has a dark custom, dating back ages to the founding of the Nine; the king must always be an outsider, and he must defend to the death in hand-to-hand combat his right to be king against any challenger. With their psychic powers, the Nine foresee the arrival of Gratillonius, weaken Colconor with a night of sexual revels, and then place Gratillonius in the unwanted position of having to fight Colconor. A trained soldier, Gratillonius slays the strong but untrained Colconor and finds himself not only the prefect of Rome but the King of Ys.
His first mission is to make Ys strong enough to hold Armorica securely for Rome while the civil war continues. To do this, he not only builds up the city's navy and defenses, but he works to make the city economically strong. He sees the life of Ys as a unified whole: The strong navy protects the city's shipping, making for secure trading with other cities; the trading makes the economy stronger, making the city better able to afford a strong military and making the citizenry prosperous; a prosperous citizenry means a happy citizenry, and good public morale means people willing to defend what is theirs against invaders and pirates, as well as people who are disinclined to rebel against Rome. These three aspects of society are often linked by historians and political scientists to the welfare of a nation, although they might differ over which of the three is the most important and how each—military, economy, public morale—is to be satisfied.