The Ghosts of Rathalla

Set in a world that is dominated by a vast desert, two friends are caught in the middle of a civil war. She's a warrior. He's a musician. When they discover that the crux of the war is a prophesied newborn baby that one side will do anything to destroy, they become the only people capable of saving the child's life—all that stands in their way is an active volcano, a barbarian army, and a cunning assassin with motives of his own.