Loki brings Jane Foster to Asgard and tries to convince Odin that it was Thor who brought her there. In order to prove which of his sons is lying, Odin sends both to Skornheim, where they must endure its deadly dangers.
Scientist Paul Duval gains the power to turn himself (and whoever he touches) into living stone. As the Grey Gargoyle, he attacks Thor hoping to steal Thor's magic hammer, which he believes will help him gain immortality.
When a race of underground lava men threaten the surface world with destruction, Thor gathers his Avenger teammates in an attempt to thwart the attack. The group is aided by an unlikely ally, their former team member, the Incredible Hulk.