Thor has broken the sword Tyrfing so that it cannot strike at the roots of Yggdrasil, the tree that binds together earth, heaven, and hell. But now the mighty sword is needed again to save the elves in their war against the trolls, and only Skafloc, a human child kidnapped and raised by the elves, can hope to persuade Bölverk the ice-giant to make Tyrfing whole again. But Skafloc must also confront his shadow self, Valgard the changeling, who has taken his place in the world of men.