Loki has seized the Odinring, making him the ruler of all of Asgard, and Thor is forced into loyalty to his half-brother to ensure that Sif remains unharmed. However, Thor argues that he will soon stop his mad brother, to which Loki decrees Thor be sequestered in the dungeons forever more, and guards attempt to take Thor away. Spying on the situation, the Warriors Three come out of hiding upon learning the news and battle Loki's loyal guards however they are soon overpowered and imprisoned.
Meanwhile, on the outskirts of Asgard, two riding soldiers come across a flaming sigil in the shape of Odin's mark. Upon their discovery, it suddenly erupts in a giant explosion. While back in Asgard proper, Thor and the Warriors Three are locked in a cell (although the guards have difficulty fitting Volstagg through the door.) They are left to their own and wonder how they might escape and overthrow Loki's rule when Balder arrives in the dungeon and sets them free. Broken out of their cell, Thor and the Warriors Three team up with Balder to go and save Sif.
While upstairs, Loki asks Sif to be his bride, a request which she declines. For her refusal, Loki forces her to battle with a female troll. While back at the magical flames, the warriors stare in absolute horror as Surtur, finally free of his imprisonment by Odin, rises from the flames and appears in Asgard. The fire demon has decided that he will destroy first Asgard, then the entire universe, marking his arrival by setting the very sky ablaze.
Sif battles the female troll at the palace until Thor and the others arrive to stop the fight. Loki is once more challenged. However, he stays his opponents' weapons once more when he uses an "enchanti-screen" to show them that he has placed Odin in a capsule and sent it to the Sea of Eternal Night, a realm for those who enter it, to sleep for all eternity. With no way for Odin to awake from his Odinsleep, Loki boasts that he will rule the kingdom forever.
Before Thor and the others can attack Loki, Surtur announces his impending arrival and begins showering Asgard with flames. When Loki realizes Surturs power, he flees like the coward he is, leaving Thor, Sif, Balder, and the Warriors Three to band together. While Thor and the Warriors Three rally troops to battle Surtur, the Thunder God sends Balder and Sif on a mission to wake Odin.