After Loki switches Mjolnir, Thor's hammer, in the middle of a battle between the God of Thunder and invading trolls, Odin imprisons Loki for a year. The trickster god escapes, however, and provokes a dispute between Odin and the giant Hrungnir, one that brings an all-out attack on Asgard as well as a one-on-one challenge for Thor himself.
