In the wake of the Storm King's fall, Ineluki's loyal minions, the Norns, dark cousins to the Sithi, choose to flee the lands of men and retreat north to Nakkiga, their ancient citadel within the hollow heart of the mountain called Stormspike. But as the defeated Norns make their way to this last haven, the mortal Rimmersman Duke Isgrimnur leads an army in pursuit, determined to end the Norns' attacks and defeat their ageless Queen Utuk'ku for all time. Two southern soldiers, Porto and Endri, joined the mortal army to help achieve this ambitious goal--though as they venture farther and farther into the frozen north, braving the fierce resistance and deadly magics of the retreating Norns, they cannot help but wonder what they are doing so very far from home. Meanwhile, the Norns must now confront the prospect of extinction at the hands of Isgrimnur and his mortal army. Viyeki, a leader of the Norns' military engineers, the Order of Builders, desperately seeks a way to help his people reach their mountain--and then stave off the destruction of their race. For the two armies will finally clash in a battle to be remembered as the Siege of Nakkiga; a battle so strange and deadly, so wracked with dark enchantment, that it threatens to destroy not just one side but quite possibly all. Trapped inside the mountain as the mortals batter at Nakkiga's gates, Viyeki the Builder will discover disturbing secrets about his own people, mysteries both present and past, represented by the priceless gem known as The Heart of What Was Lost.