Bleak Seasons: The Sixth Chronicle of the Black Company (GLITTERING STONE/GLEN COOK, BK 1)

This is the harrowing tale of the defense of Dejagore, as told by Murgen, a seasoned veteran of many brutal campaigns. The Black Company has taken the fortress of Stormgard from the evil Shadowlanders, lords of darkness from the far reaches of the earth. Now the waiting begins.
Exhausted from the long siege, vastly outnumbered, and beset by powerful sorcery, the Company have risked their souls as well as their lives to hold their hard-fought-for prize. But this is the end of an age, and great forces are at work. The ancient race known as the Nyueng Bao swear that ancient gods are stirring. The Company's commander has gone mad and flirts with the forces of darkness. Only Murgen, touched by a spell that has set his soul adrift in time, begins at last to comprehend the dark design that has made pawns of men and gods alike.