Author's note: I had to write this because my hands wouldn't keep still until I did. And no, I'm not randomly obsessed with fish: have a quick read of the edda to know why. Absolutely jam-packed with spoilers for The Dark World.
One rule, and one only: never do as is expected of you.
There are patterns in all things: inside the bole of Yggdrasil, in the ripples that surround the leaping salmon, in the gnarled horn of the goat. Nature loves a pattern to follow.
When young Asgardians are first taught to fight, they are taught thusly. The rules first, then the correct application of them. Every fight begins as a pattern, like a dance of steps. A dance towards death - the death of the other, of course. But in learning a pattern you learn also to measure a risk.
Stick to the pattern, and you become predictable. The fisherman, as anyone knows, follows the ripples to trap the hiding salmon. The good fighter knows every step of the fight as it should be, but the great fighter knows that to win you need to take a few of the steps out of turn. Anticipate, adapt - and win. Conform, be inflexible, and lose.
"Betray him and I will -"
It is the most predictable thing in the world for the god of lies to deceive you. It is his nature. And there is something just so innately untrustworthy about Loki: he exudes duplicity so plausibly that even on casual acquaintance one feels he is neither safe nor tame.
There's a moment where the creature's fired, berserker eyes meet the cool green of the man in the cell. It has released the others. Mad beasts, all. Mad beasts may be trusted to rampage, slay, howl and murder, and as this is what is required of them, all is well and good.
But this is not a mad beast.
They stare at each other through the humming barrier. Inside the cell all is calm. An elegant chair, a small collection of books. Even the air is purified, lest any small insect coming in be grist to Loki's magic. Outside the cell the air is hectic with smoke and the musk of fear. The creature's own sweated breath clouds in it.
No, he will not release this one. This one would betray him.
And Loki knows all this is to his advantage, and indeed just as he wanted it. So he tells the creature the way forward, freely.
"I believe there will be a line."
In New York, Loki crossed a line. Thor wants to believe that his brother is still in there. What he doesn't want to believe is that there is no "in there".
He doesn't want to believe that this is what his brother truly is. So to cushion his love and his ego he looks for patterns, familiar ones, and when he finds Loki in crumpled grief, still locked in his cell amongst his shattered possessions, he finds them. And from then on, it is a fairytale simple enough for children. Just as nature creates patterns, so we, created by nature, make patterns in our lives with stories. Archetypes are created by them, lives are governed by them. Brothers parted by power come together for family. For love. And because it is how these things work, the god of lies betrays his brother once again for power. The creature locks eyes with Loki once more, feels the roiling miasma of spells and deception around him, and knows him for a villain.
Loki merely hopes that Thor stays true to his nature and keeps in his furrow like any good plough, clearing the way for things to come. So when Malekith feels the thread of the child's fable unravel before him with Loki's double deception, and Thor rise with hand intact, Mjolnir hitting his palm with a ringing slap, it is really only natural. One may always rely upon the god of lies to deceive.
"Oh dear. Is she dead?"
Perhaps what should have given Thor pause for thought (but did not) and Jane cause to doubt (but did not) is that it is not in the nature of the god of lies to protect anyone except in service of himself.
Loki protects like the mother of a litter of wildcats as the wolves close in. He is a demon in his rage, dagger in hand. The svartalfar believe themselves surrounded by snarling beasts and kicking horses as Loki's magery strikes into their minds where they cannot shield. Jane looks up, once, in the heat of it all, to find him crouched above her, wild-eyed, bearing the brunt.
And it is time now for Loki to tie up the faltering threads of story, to re-weave the pattern, to be reconciled with his estranged brother in the blood of his enemy. The creature, for its part, feels at the deep centre of itself, beside the mortal wound, beside the gently flickering time-bomb, a justification: it had judged rightly, not released Loki itself. Such a man is too dangerous to be wielded like a weapon by others. He is too unpredictable. It dies knowing that it was right. Loki dies knowing the same.
"I'm sorry. I'm sorry."
One rule, and one rule only. Never do as is expected of you - unless it is the only way to achieve the unexpected. Loki dies in regret, which is expected. Thor weeps in forgiveness, which is expected. It is the most predictable thing in the world for a villain to redeem himself in the manner of his death, and his family weep for the erstwhile black sheep. But one must be oh-so-flexible in what one is willing to be and willing to do. One must do the only thing that will be accepted.
Sometimes the salmon escapes the net: sometimes the salmon isn't even a salmon, in truth. Loki will be anything, do anything, in order to win. Even if it means going beyond predictability and into pure showmanship.
After all, it's hard for someone to kill you for betrayal when you're already dead.