Title:The Law of Conservation of Energy
Universe:Supernatural
Theme/Topic:N/A
Rating: PG-13
Character/Pairing/s: light DeanxCas, Sam (appearances by Bobby, Crowley, Balthazar, and Raphael)
Spoilers/Warnings: Spoilers through 6x20; AR after that.
Word Count: 90,030
Summary: The law of conservation of energy states that energy cannot be created or destroyed, only transformed from one state into another. And what is grace, if not energy? In order to win the war in Heaven, Castiel and the Winchesters embark on a cross-country quest to find the scattered shards of Gabriel's grace in the hopes that its remaining power will be enough to defeat Raphael.
Dedication: for my awesome beta mclachlan, my amazing artist artmetica, and with special thanks to sophiap for giving this a once over for me as well. Also, with love to Sonia and Emily for letting me drag them on board this crazy train with me.
A/N: Guys, you will never know how lucky I am to have all of you; there is no better cheerleader than mclachlan, because without her I definitely would have cowered in the safety and comfort of my Impala fic and while this fic is a genre/style/length I'm not really so very comfortable with, I think I'm better for having tried it. As for artmetica, you will not believe the bombardment of texts and messages I got when it was discovered she picked me; I think it's a lot like finding out from your friends that you won a prize in some amazing contest that you only entered for shit and giggles and never expected to win. I hope my story lives up to this ridiculously great (and prolific) art!
Disclaimer:No harm or infringement intended.

Prologue

"Next to Sam, you and Bobby are the closest things I have to family. And you are like a brother to me, so if I'm asking you not to do something, you gotta trust me, man."

Castiel stops at that moment, at those words, eyes trained carefully on Dean as his friend stands in front of him, imploring him. The human he has done everything for—given up everything for—pulses with a white hot anger Castiel can feel erupting outward all the way from his grace. For a moment the angel balks at that, at the heavy sensation of being judged by this person, by this puny, mortal man who does not understand—cannot comprehend—the things Castiel has done and lost and suffered for his sake. What can a human know of him, an angel who has seen eternity, who has all the knowledge of the universe at his fingertips? Dean has no right to judge him. Dean can never fully grasp the gravity or the vastness of Castiel's existence.

He is just about to say so, is going to instinctively snap that he will continue on with or without Dean's approval, that Dean cannot stop him because, in the end, Dean is nothing but a man. But when Castiel looks into Dean's eyes, he feels himself stop suddenly—feels the world and his bitter words stop with him— because he sees something else there as well, something small and warm sparking faintly under the waves of Dean's disbelieving anger and roiling betrayal. It is a familiar and unexpected creature that he discovers in the shadows of Dean's eyes in that moment, a thing as thoroughly killed and implausibly resurrected again and again as Castiel has been himself.

It is faith. It is a full and hopeful belief that Castiel had not expected to see from this man ever again, especially not at this moment, as they stand, just the two of them, under Bobby's roof in the quiet dark of night with all the angel's secrets finally laid bare before them.

And somehow still, despite all these things, the hope Castiel sees before him burns white hot. It is the kind of faith that Dean has not showed in many years, not even when he had fully pledged himself to the service of the angels and to Heaven, only to be trapped in the green room and made to sit idly as his brother unknowingly destroyed the world. This hope is inexplicably strong for such a small, terribly battered thing.

Castiel realizes suddenly that somewhere, underneath all of the anger and the betrayal and the wounded disbelief, Dean still believes in him.

And as Castiel looks at Dean and knows this, as the tension grows thick between them in the silent room as Dean waits for the angel to answer, Castiel feels the words he wanted to say die in his throat abruptly, fading back into nothingness at the pull he feels in Dean's eyes, at the belief he feels calling quietly out to him—pleading with him— from Dean's soul.

Castiel finds himself with a choice. How strange that as an angel—a creature made to obey— he has been forced to make so many.

He knows very well if he gives in, if he acquiesces to Dean's desires as he too often does, it will mean everything he's worked so hard for over these past two years will become nothing. He will have fought and incited and razed and cheated and lied and killed—sometimes outright murdered— for no reason at all. Just because Dean would want it.

At the end of this moment he has two options. If he chooses the first, his cause will be greatly weakened. He will be shunned by his brothers, left with nothing but the faith of a weary Righteous Man and another uphill battle against the combined forces of Heaven and Hell, all out to destroy him, to destroy the world and everything he had already died to save.

But if he chooses the other, Dean will hate him.

He feels his shoulders slump slightly as he stares at Dean—the belief he sees there, the tinny flare of hope— and already knows his answer. His decision is made.

It is the word which will send his war efforts tumbling to the ground at his feet. It is an answer which has the power to erase nearly two years of progress—two hundred years in Heaven and Hell and countless brothers and sisters dead— like none of it had ever happened. Like none of it ever mattered.

Castiel tells himself two years, two hundred years, are of no consequence. Millennia upon millennia are of no consequence.

He has lost far more for this man before. He once gave up an eternity for Dean.

"Cas?" Dean murmurs as the silence echoes onward, and he is still angry, now fearful. The flame of hope in him sputters, weakened.

Castiel does not look away from him when he answers.

"As you wish," he says.

And that is all.

He closes his eyes as he feels his empires crumble to dust with those three words. Everything is suddenly gone, swept away in the wake of choice. Beside him, Dean breathes a sigh of relief, exhales a jumble of words that might be, "Thank you." Hope flares bright and warm.

The sound of them—for the moment—makes Castiel forget all which has been lost.

For now, he still has this.