The Time of Troubles: Bk. 1 by Harry Turtledove
The uneasy peace between the Empire of Videssos and the nation of Makuran was crumbling. War came, and the King of Makuran lay dead on the field of battle. Worse, a power-mad minister had seized the throne and the rightful heir had disappeared. Abivard, son of a Makuran lord who also had fallen in the same battle, realized that his only hope of saving his family and his land was to find the missing heir, though that would mean he would be branded traitor and become the target of every armed man who served the usurper - and of his nation's most powerful sorcerers.