The God in the Moon — Richard A. Knaak

As a favored son in one of the high families of Aquilonia, Nermesa Klandes wanted for nothing -- except glory won by his own hand. Defying his family and casting aside the opulence he was born into, Nermesa joins the Aquilonian army so that he might serve his liege, King Conan.

But Nermesa soon learns there is a great distance between his courageous idealism and the gory battlefields of the Westermarck, where the savage Picts wage unceasing warfare. Through bravery and cunning, Nermesa comes into his own as a warrior and a man. When he kills the Pictish leader, he is hailed as a hero. But he also unleashes an unholy power that will shake the very foundations of the Aquilonian Empire...