To defeat Thor, the Norse god of thunder who has killed scores of innocents, Viking vampire Leif Helgarson teams up with Atticus O'Sullivan, the last of the Druids, a werewolf, a sorcerer, and an army of frost giants.

"Thor's hammer is missing again. The thunder god has a disturbing habit of misplacing his weapon--the mightiest force in the Nine Worlds. But this time the hammer isn't just lost, it has fallen into enemy hands. If Magnus Chase and his friends can't retrieve the hammer quickly, the mortal worlds will be defenseless against an onslaught of giants. Ragnarok will begin. The Nine Worlds will burn. Unfortunately, the only person who can broker a deal for...