Ragnarök: The Breaking of Helheim (Ragnarök: The Breaking of Helheim #3)

As the Great Enemies plot to destroy the God of Thunder, the last of their ancient foes, Thor fights to free slaves laboring in a deadly mine on the rim of Helheim, the kingdom of the dead. The recovered ore is being turned into magical sword blades that will enable the despotic ruler of the upper levels of Helheim to conquer the Dusk Lands with fire and blood.