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.