Sort of pre-slash frostiron (that's Tony/Loki if anyone was unaware) so if you don't like that, I suggest you turn back now. The first and third chapters are kind of small compared to the second so sorry for my inconsistencies.

The Avengers belongs to Marvel. The title and chapter names are from Take Back The City by Snow Patrol.

Chapter 1: Take Back The City.

The Bifrost, the observatory, and the inter-dimensional portal have only just been rebuilt, after endless months of toil, and Heimdall only just taken up again his watchful gaze of the realms, when it happens.

A darkness, an intangible mass of black, silent and freezing, surges up furious and hungry from Niflheim, engulfs the observatory and cloaks Heimdall, causing him, for the first time, to lose his sight. It billows out onto the new Bifrost, spilling towards the city of Asgard, turning the lights of the rainbow bridge dark, the warmth of it cold.

Odin, Thor and the army of Asgard rides out to meet It although they know not how to stop It or fight It; It is incorporeal and therefore cannot be touched by sword or fist. The blackness swallows up many soldiers, and they fall dead off of the Bifrost and away. Thor attempts to punch Mjolnir through it, but it simply glides through, and sails back to him covered in something that looks like soot and burns to the touch.

It is, as is always the way, at the last moment when all seems truly lost, when it happens.

From within the centre of the thick smoke, or mist, or blackness, a crackling sound begins. Odin pauses, so Thor does, and then the soldiers.

The noise grows until it becomes apparent that ice is spreading out from the middle of the thing, until the entirety of It is covered, encased, imprisoned by thickest ice. And then, with the force of a small bomb, It shatters on all sides, if It had sides, the shards flying out in all directions, soaring into the navy void beneath The Realm Eternal. The Bifrost is almost blinding as it lights up once more.

And there, where the middle of the Thing had been, their savoir stands amid the glow.

Loki Laufeyson, God of Mischief, wayward adopted son of the Allfather, war criminal of Midgard and shamed prisoner of Asgard.

His skin is the hue of the Jotuns, his eyes deep, deep scarlet, and in his hands he clasps The Casket of Ancient Winters. He makes a quick hand gesture and the Casket disappears, and Loki stumbles toward the citizens he hates, who hate him.

His skin bleed back to Asgardian pink, his eyes their sharp green, and as he comes closer, they see the state of him; he is drenched in sweat, his skin bleached of all colour and is clearly exhausted from battling his confines within the imprisonment building of Asgard. The exertion of attempting to teleport out of his magic-dampening cell has resulted in a nose bleed. His wrists too are bloody, where the runes that also diminished his magic, carved there by Odin, had bled as their hold was broken.

"Heimdall will regain his sight soon enough." He rasps almost inaudibly. "Any being spawned in Niflheim would fear and meet its destruction in the ice whence it was created."

He half-walks, half-falls towards Thor, and holds out his quivering hands. "Mjolnir, hand it to me." Thor looks apprehensive and quite untrusting. "I seek to rectify what has happened to it. Hand me the hammer." Instead, he simply reaches for it, grabs it with both hands and lifts it out of Thor's grip. Thor looks on with a kind of horror. Loki gives Thor something that could not even count as a smile, it is too awful. "I have not become worthy, never fear. Tis simply not so heavy when tainted with darkness."

Loki runs one faintly blue hand over the hammer, muttering under his breath until the darkness seeps from it. Loki pitches forward violently with the sudden return of weight to it, but Thor catches him, places Mjolnir gently on the Bifrost, and scoops Loki up into a hug. "You have saved us, brother!" He cries, joyous, until Loki's whole body grows impossibly hot in his arms, and he frees him with a gasp.

The look on Loki's face is horrible; it's ugly and warped with utter loathing. "Do not touch me." He hisses darkly.

Thor steps back, wounded and slightly appalled. But before he can say anything, another voice speaks.

"Loki."

The strangely soft voice of Odin.

Loki turns, his face impassive, and walks up to the King, who has dismounted Sleipnir. When he reaches him, he draws himself up to his fullest height: long, lithe, and compared to Odin, young, Loki seems to tower over the Allfather.

He inclines his head in a mockery of respect. "Allfather. If you are going to ask me for the whereabouts of the Casket, you shall be disappointed, for I shall not divulge. The Casket belonged to Laufey, and now it is mine. Or are you going to bade me a new punishment?" Loki proffers his bloodied wrists out to Odin. "As is evident, I broke your binds. I can scarcely believe you imagined you could keep my powers from me indefinitely. So what now, Odin?" Loki grins, like something is hilarious to him alone. "Would you be brave, and have me executed, finally?"

Loki continues to smile in a smug, insolent way that would earn a younger child a hard slap but Odin does not rage, Odin does not castigate. He merely whispers, "My son."

It is two words, two simple words, but it is all that is needed, and Loki completely loses it.

So virulent is his fury that his Asgardian guise is totally stripped away, his hair flying, his skin deepest blue, the markings of Jotunheim standing out against his skin, his red eyes blazing with hate and wrath and despair. His lips curl back over his clenched teeth, and he opens his mouth and Loki screams in a voice that sounds hauntingly like Laufey's:

"I. AM. NOT. YOUR. SON!"

And then with a sound like the universe ripping in two, a blinding flash of green, and a bang, Loki is gone.