Loki’s usually impregnable lone fortress suddenly faces unexpected visitors as the artificially grown Frost Giants break down its door, wanting the cold Loki has created. Angrily, Loki blasts them with his magic. Barely deterred, the giants wish to kill him and take the cold. Loki flees, realizing his plan to assist the Frost Giants has gone amiss. The cold not only restored their original height but has driven them mad. He shuts a door and reinforces it with a spell of binding.
He hurries past his unconscious step-brother, Thor, whom he transported here before the Dark Elvish warrior Grendell could kill him. He grins, recalling that not only are Thor’s bones more brittle, but thanks to Hela’s curse he also cannot die. Let the giants play with a new toy, while he arranges their defeat, Loki decides and teleports Thor (without his hammer) among the giants. Loki calls out from behind the door this is a present to them.
Loki enters the room where the machine is, only to find the room chilled, the machinery frozen solid, and more ice is forming by the moment. His prisoner, Iceman, is trying to overload the cold enhancer that holds him captive, which explains the giants’ madness.
Loki orders him to stop. The cold he is generating will summon the frost giants. Iceman ignores him and gives it everything he’s got.
A few halls away, the giants have gathered around Thor, arguing on whether to wait for Thor to wake up before killing him or not. They sense the increased cold and grow larger again. Wanting more like drug addicts they follow the trace of the cold, forgetting about Thor.
However, Loki stands in their way, forbidding them from going any further. He sends a magical fireball at Grundroth’s people which serves in melting some of them. The others smash the sides of the hallway to flee before they perish. The flying debris destroys the fireball, after which Loki loses his footing and falls.
As the giants take Loki prisoner, Thor awakes, moaning at the agony of his broken bones. The last thing he remembers is the fight with Grendell. He soon realizes he is in Loki’s castle keep. He watches the frost giants overwhelm the struggling Loki and feels regret and shame. Loki’s bravery before impossible odds reveals his own disgrace. Woe that the thundergod should ever have to flee such foes as Grendell and the Absorbing Man! Loki is but the son of giants. Thor is the son of gods!
In Asgard, new king Balder converses with the sage Ularic, who warns that the stars foretell great danger for the realm. Before he can continue, the wise man sinks down in weakness.
Balder calls for a guard, but instead Heimdall stumbles in, carrying the unconscious Enchantress. Heimdall warns the guards cannot hear him any longer. He continues that the Enchantress has become hard as stone and he too has caught it and feels his limbs failing. The desperate Balder wonders where Thor is, even as he senses his limbs stiffening as well.
In Loki’s castle, the giants surround the unconscious Loki when suddenly, without warning, the walls drop on them. The giants flee, unaware that Thor is behind this.
Thor regains his hammer and finds Loki was protected from falling debris by a giant’s body. Thor drags Loki onwards, telling his unconscious brother that, even though he can barely stand, he will stay the course. He muses that after all these centuries the fosterling of the giants taught the gods a lesson in courage. He knows Loki didn’t bring him here for any good purpose; nevertheless he saved Thor from the Dark Elves.
As he enters the lab, he senses the cold and finds Iceman in his human form. Thor recognizes the costume, as he met other X–Factor members days ago in the Morlock Tunnels.
As Thor gently helps him down, Bobby recalls what Thor did for Angel. Does he make a habit of saving them? Thor tells him this time he doubts he could even save himself. How did he come here? Bobby tells him how Loki bragged about his device. Iceman generated more cold than Loki liked, more than he ever did before. Exhausted, Bobby falls unconscious.
Thor hears the giants closing in and realizes the door will not hold them. From Bobby’s description, Thor recognizes the great machine that once brought the Absorbing Man to Earth long ago. Thor has not forgotten that, were it not for Loki, there would not have been a final victory over Surtur. Today, Loki taught Thor a lesson in courage, maybe in turn Thor can teach him one of honor. And win or lose, that debt shall be paid.
Thor aims the teleportation device towards Midgard, namely the Pittsburgh steel foundry where he forged his new armor and teleports it to himself. Before it arrives, Thor stomps his hammer to finish the spell he began on Earth. Only fires wrought by Mjolnir can create the heat necessary to emblazon the sacred runes of Odin upon the metal. He whirls Mjolnir and, as the armor manifests around him, the ancient symbols of power are inscribed upon the armor.
In the meadows outside Asgard, Fandral, Hogun, Sif and Hildy also suffer from the weakness while the human twins Mick and Kevin watch nervously. As Sif falls, the boys begin to cry. Hogun tells them to be strong, so the boys try to help Hildy along. They are greeted by ominous silence and find Volstagg and his family also unconscious from the strange illness. Only the human boys are left standing.
Meanwhile, in Loki’s castle, the Frost giants smash the door to find Iceman and Loki lying in the rubble. They soon realize Iceman is the source of the cold. A mortal, they marvel.
So he is, Thor in his new armor announces, and that places him under his protection!
They don’t recognize him at first, which quickly changes when he throws Mjolnir at them. He presses his attack but the giants know about his vulnerability.
However, they attack in vain, as his magical armor now has become his body. And the frail flesh and bones within command it even as they once commanded the body that was whole. He smashes Mjolnir to the ground. The shockwave fells them and he swings his hammer, using the stone debris as weapons against the frost giants.
The surviving frost giants flee, vowing vengeance. Instead of triumph, however, Thor fears that before long his heart and soul will be tested.
As the giants huddle in the cold, they fear there is nothing they can do. Their leader vows vengeance. No giant living can withstand Thor but he is not thinking of a giant but the offspring of one: Loki’s child Jormungand, the Midgard Serpent. The others protest it’s too dangerous. He tells them shut up. Nobody mocks the sons of Ymir. In the end, the Nine Worlds will be theirs to plunder and Thor’s bones will be dust, he promises.