Pleased to thank Molly-Myles for her excellent Beta work on this.

It was, as it always was, the nightmares that kept Dean alert. Factually, he knew that his life should scare the living crap out of him. He himself had, on many occasions, pointed this out; to his brother, to strangers, to overzealous victims. But the honest truth, regardless of whether he chose to admit it, was that his life – the constant battle against death, brutal odds, the forces of both the Attic and the Basement – did not frighten him. The things that frightened Dean Winchester made a very short list, and monsters of the night did not make the cut.

As far as Castiel had ever made out, the list was limited to the following:

1. Losing his brother, Sam.

2. Returning to Hell.

3. Failing his self-assumed duty and letting the Earth be obliterated.

Castiel knew all of this, because Castiel knew Dean. Though the human had never dwelt on the matter, when Cas had dragged Dean's soul (broken and loathsome though it had been) from the pit of Hellfire it had been trapped in, he had seen into parts of the man that Dean himself refused to acknowledge. To human eyes, the burn of Castiel's touch had faded from Dean's shoulder, but to the angel it still glowed, forever branded upon his soul. It was evidence of that bond, of Castiel's dive in damnation. No matter that the humans were so blind, the celestial creatures could see the claim that Cas had laid on Dean's soul, the part of his Grace that would never leave it.

Until recently, Castiel had felt safe in adding his own name to the list, that Dean feared losing him too. But it was all broken now. There was no affection in his words anymore, and Castiel could not detect the comfortable patterns in his thoughts that had previously accompanied their shared companionship.

It was hard to think this way, for the angel. His mind was aeons old, and moved much faster than the human concept of time allowed for, but what had once been sharp as a blade was dull, and full of madness. The scarlet floodlight that filled Castiel's head now was not his own, but it affected him as if it were. That was the price that he had paid to free Sam Winchester of his mistake, although it made little difference to him now. All thought, all emotion melted under the intense crimson flames, bubbling like flesh drenched in acid.

Occasionally, Castiel would skim through the part of his mind that remained intact, the tiny clearings of rational thought that allowed him to understand fully his dire situation, and the guilt that rested on his wings. Burned into Dean's entire being as it was, it came as no surprise to the angel that the rational parts of himself resided close to the human.

Now, he was very close to Dean though his rationality was questionable. When he had agreed to this farce, he had suspected he was wandering the edge of a clearing, only partially lucid to his reasoning. Whatever his motivation had been for accompanying the Winchesters on their way to end the Leviathan King, he could not remember now. His vision wasn't entirely clear, though the grotesque visage of the monster before them was unmistakable.

Had he not been divine in origin, Castiel may have said that the Leviathan King's face was oddly attractive. Not in the sense that humans seemed to understand, but in a more literal fashion; twisted and jagged though it was, it could have held a sort of fascination to the fallen and insane angel, drawing him closer for more thorough inspection. Castiel was, nevertheless, divine in origin, and his Grace – warped though it had become, cut through with bleeding red scars and pitted with the dark stains born of his fall – kept his eyes clear of such deception. The Leviathan (King or otherwise) was an ugly creature to behold, and Castiel wished with every ruined part of himself that he could not see past the vessel, the form it had chosen.

The creature, teeth glistening in its eerily angled face, the face that Castiel saw so clearly behind the human façade, was grinning. Understanding was a blurred concept to Castiel, his thoughts so defiled by the constantly pulsing red light, but the sight filled him with a horrible sensation. It was one he couldn't quite place, one that had been utterly foreign to him before his rebellion, before his fall. It was a feeling that oozed, slowly enveloping his entire being, vessel, Grace and all.

No, Castiel certainly did not understand it, and what he wanted more than anything was to 'blip out', as the Winchesters had termed his flight, to flee the terrible creature. He could almost hear the buzzing of insects, so beautiful and uncomplicated that they were. Bees, in particular, were of much interest to the angel. They were so tiny, on their own, and yet somehow they each performed a small task that added up to such perfection. That such a horde of individuals could act so completely as one being and produce that which had not previously existed – this being honey, concerning the bees – was incredible. It seemed to dull the cruel scarlet in his mind, bringing him a small measure of peace and the pleasant white that he used to think with; diluted to a sickly pink.

However, he could not leave. The tattoo of his old Grace was scorching on Dean's shoulder, blistering white filtered with cold blue. His thoughts, as they were, wrapped around it, the fragment of what he had once been, and the man that it was attached to. Protecting Dean had always been his foremost concern, ever since the moment he had been risen from perdition.

Angels didn't have souls, not in the way that humans thought of them, not in the nuclear-explosion-waiting-to-happen way. But in the same manner, humans did not have Grace. To an angel, their Grace equalled a human's soul. When Dean's soul, raw and unbridled by physical form, had been gripped by Castiel – Grace at full force and surrounding him in a protective veil, preventing him lasting harm from Hell's fire – they had touched. A piece of Castiel would always be present within Dean, and though it was not the same, the imprint of Dean's soul would never fade from Castiel.

In a way, protecting Dean was protecting himself, but it was more than that. Dean and Castiel's bond was rare and unrivalled. It was almost base instinct to the angel. Castiel's Grace equalled Dean's soul, and vice versa. And that light, that brilliant star that was contained in the fragile skin and flesh of humanity, was threatened.

So it was when the Leviathan, arrogant and sure its own victory, stepped towards Dean. Cognitive thought was beyond Castiel's capability, but Dean was in danger and he stepped forward. No matter the cost, Castiel would protect Dean, would prevent as much harm as possible. It went beyond his friendship. Rescuing souls from Hell had been prohibited of the angels for uncounted centuries. Had the red light allowed him to, Castiel would have understood why, now. Angels and humans were never meant to bond in that manner.

He had no weapons, and he could not even see properly beyond the faces of his enemy, but Castiel moved more quickly than his human vessel was otherwise capable of, his Grace demanding the strain of the flesh. Before the Leviathan could lay a hand on Castiel's human, he was right there, in the way.

And then, with a flash of white tiles and pain, he was not. The boxes broke underneath his body – rather, Jimmy's body – and ill-informed pain tried to invade his nervous system. Oxygen rushed out of the delicate lungs, and Castiel could have cursed the need for air that he had within Jimmy's form. But every sense that was his own – the galaxies of sensation that existed outside his vessel, that stemmed from the creature he truly was, wings and all – strained towards Dean, and the part of himself that was still pure.

By the time that Castiel could see once more, all of his visions full of red static, the Leviathan was extracting a bone from its chest. Castiel's divine senses informed him of the sins that lay upon that bone, neither righteous nor dangerous. It snapped with a resounding crack, and he flinched because his vessel was accustomed to that reaction.

Something important swam through the crimson sea in his mind. That bone had not been the powerful weapon that the Winchesters had prepared. Cas could see it even now, being revealed by Dean to the hastily triumphant Leviathan, spotless and just.

Hands moved, muscles flexed, and Castiel wrenched back on the Leviathan's hair, forcing an opportunity. Leviathan may be able to slaughter angels on a whim, but Castiel's strength was not to be scoffed at. Exposed like that, and taken off guard by the diversion, the Leviathan King could not react in time to stop Dean. The true weapon, soaked in the blood of the fallen, pierced the creature's throat and held.

Castiel did not see the expression on the Leviathan's mortal form. He only saw the nauseating rage that turned an already monstrous visage into something that Castiel may have seen in nightmares, were he capable of experiencing them. It literally pulsed from the King, entwined with its death throes.

The air shimmered with the creature's power, so much so that even the humans observed it. And even then, the Leviathan grinned in cruel victory and Castiel knew – the lucidity exploding in his mind like holy fire – that they had miscalculated. In some way that they had not foreseen, Castiel and Dean and Sam had been gravely mistaken. And now, they would pay the price.

Finally, the enemy died, its terrible form disintegrating with a mighty noise and the splatter of black.

Castiel was dizzy, when he found he could see again. For just a moment, the parts of him that were not all angel won out and he stumbled, dropping to the ground. He had felt the slight pangs of nausea before, when he had found himself in the presence of the archangels, but this was a different sensation. For a second, he found himself wondering whether he might experience vomiting.

However, the dizziness passed and as his vision steadied, Castiel became aware of several things. First and foremost, he savoured the slightly unfamiliar way his thoughts aligned themselves in sleek clarity. Whatever the madness was he'd lifted from Sam, whatever the red floodlight that had corrupted his mind, it was gone. For the first time in a while, Castiel found he could think clearly. It was this which allowed him to fully comprehend how dire his situation currently was. Without the crimson haze clouding his senses, he could already pinpoint the souls around him, and none bar one were friendly.

Most of them, oily and hungry though they felt against his Grace, were of a lesser concern to him. It was the black ones, sharp and ravenous and already nipping at his Grace, that worried him. More than that, if he was honest; there was a spike of fear in his belly that Cas was unaccustomed to feeling.

He had always wondered why taking a vessel had been criminalised before he had rescued Dean, but he thought he knew better now. Remaining within flesh, being bound by bones and chemicals… No matter how one's Grace protected one, eventually aspects of humanity took root. Emotions became stronger, goaded by physical responses that angels alone lacked. Of all the emotions Castiel was forced to accept, fear was one of the ones he loathed the most. It was an emotion that stripped him of logic.

The fear that the black souls inspired in him was in and of itself terrifying. The urge to flee was almost overpowering.

"Dean," he called out quietly, trying to attract as little attention as possible. It did not matter what actions he took, Castiel's Grace was so alien to this place that it felt pure in comparison, even though Cas knew it to be anything but. Castiel himself was a beacon, a seraph, divine, in a place of such unparalleled corruption. Anything would find him. Everything would find him.

And the Leviathan were the most dangerous creatures to reside here. That they even did informed Castiel of precisely where they were. If the malicious atmosphere hadn't been clue enough, he could sense no human life, nor angelic life, nor even demonic.

Purgatory was a dangerous place for monsters. Castiel could only imagine what they might want to inflict upon a human. But an angel would be an even greater prize, should they catch him. Most of the monsters here posed little threat to him, but the Leviathan were an entirely different matter. Already, they were closing in, their aura of fear preceding them. And Castiel, he realised, had just aided in slaughtering their King. The bounty on him would be immense.

"Wake up," he tried, walking closer to the man. Dean lay on the ground, surrounded by leaf litter. Extending in every direction around them stood bare trees, skeletons of themselves in the darkness. And above their heads, stretching beyond even Castiel's eyes, a blank sky, dark and empty as a slate.

Dean's eyes opened, and he sat up slowly, taking in their new environment. Whether in response to that or whether he could miraculously sense the danger they were in, Dean's emotions tightened. "Good," Castiel said, knowing that Dean couldn't read his mind, and feeling the need to verbalise his relief that the human was able to run for himself. The Leviathan were still closing in, and though other souls with evil intentions were far closer, even they would flee should the black creatures arrive. "We need to get out of here."

Dean would go nowhere without information, and Cas was painfully aware of that. He could feel his heart rate accelerating (a strange human sensation that still seemed so illogical to him) in reaction to the terror creeping through him. Just once, Castiel hoped that Dean would run first, and demand answers when they were safer.

But alas, as Dean stood and looked around him in cautious confusion: "Where are we?" His words came out in puffs of steam in the increasingly icy air.

Cas was honestly surprised. Dean was a highly intelligent person, and surely even he, though human, could sense the malevolence that surrounded them. At the very least, he had expected Dean to have an idea of what had happened. "You don't know?" he replied, seeking confirmation. Surely, Dean was toying with him.

Of all the times for Dean to use his 'sarcasm', if that was what was occurring, now was less than ideal. The Leviathan – three of them, Castiel guessed – were nearly upon them, greedy, and their fearful aura was even starting to affect Castiel's respiratory functions.

"Last I remember, we ganked Dick," Dean informed him, his eyes flickering slightly in what Castiel had come to recognise as confusion. Reading emotions wasn't difficult, thoughts and motivation even easier, but five years in a human body had taught Castiel how to read body language. Frankly, though, Cas had no patience left for Dean's humanity.

The Leviathan were close, and death was at their heels. "And where would he go in death?" he countered, wordlessly demanding that Dean use his own, always surprisingly sound logic.

Dean's eyes narrowed, filthy brown in Purgatory's ominous gloom, and he hesitated for a moment. He was going to question the conclusion he'd clearly just arrived at, and Castiel quickly prepared the right words to cut across with. They didn't have time.

"Wait, are you telling me th—"

"Every soul here is a monster," Cas confirmed, and he was unable to not look off to his right. The Leviathan who had already found him had joined forces, and the fear was almost like a battering ram against Castiel's protective Grace. "This is where they come to prey upon each other for all eternity." Perhaps a little unnecessary of him, but Dean was wasting far too much time. Castiel felt marginally better adding the words when Dean clearly needed nothing else.

He regretted it, just a little, when he heard the horror in Dean's voice. "We're in Purgatory?"

A rustling drew both their attention to the side. A creature – a soul that was almost insignificant to Castiel's mind – had come close enough to trigger the human senses they had, both fleeing the Leviathan and hunting them.

"How do we get out?" Dean demanded, and Cas heard the slight indication of caution turning to fear in the words.

But the idea was ludicrous. Purgatory had been created by his Father to keep things in, to cage beasts that could annihilate the rest of Creation. On their own, they were not getting out. Leviathan could not escape without outside help. What prayer had they of accomplishing that? Out of respect for the impossible things that Dean Winchester had done before, Castiel kept the absolute certainty of failure out of his words. "I'm afraid we're much more likely to be ripped to shreds," he said instead, looking around sharply. The rustling was on both sides now, small little creatures that only smelled food.

They did not alarm him.

He could see, from the expressions on Dean's face and the thudding of his mind, that they did alarm the human. But even the low growl, something that may have caused the angel pause once, did not. Dean turned to look at the sound's source, fear and trepidation obvious in his slightly lowered posture, and Cas felt a spark of sorrow.

Smothered by the fear, and feeling it truly touch him as the Leviathan's proximity finally punctured his Grace, Castiel did the only thing he could think of. He had known that this course of action was coming, but he had hoped to tell Dean more before it became necessary. If only Dean hadn't asked questions. By now, he could not protect the human. He would be lucky to make it out of the confrontation alive himself. The growls of the smaller creatures did not bother him. Castiel was more than confident that Dean could defend himself against those souls, and even more so with them contrasted against the Leviathan.

Castiel fled, teleporting as far as he possibly could, allowing the Leviathan to feel a flash of his wings as he passed them by. He had to ensure they followed him. But he also didn't want to fight, because Castiel would surely lose.

Dean could survive the creatures he was met with. They were weak, nothing in the shadow of the Leviathan. If Cas had stayed, then they would have died. Both of them. And somehow, even in Purgatory, the thought of Dean dying set Castiel's wings ashudder.

He landed in a flurry of movement, the speed of his flight sending the fallen leaves into a tornado around him. But the Leviathan were fast, faster than he had ever anticipated, and their surrounding fear drove into him even as the foliage settled. Breathing deep, Castiel stretched his immense black wings wide again and picked an arbitrary direction. Fleeing anywhere away from Dean was good. In the distance, he could still sense the human's soul, beating faintly in the otherwise sea of evil.

Taking off in the opposite bearing to Dean, Castiel flew as far as he was able once again, covering more distance than the Earth could boast. Still, it wasn't enough. Already, Dean's soul-signature faded from his senses, and after a third bound Castiel no longer knew for certain which direction he should fly in.

And the Leviathan tracked him angrily, further away now but still giving chase. For hours, until the charcoal slate of the sky began to lighten into an endless expanse of cement-coloured cloud, Castiel flew away from the creatures hunting him, until he was utterly disoriented and his wings were sore. Every time he even thought he sensed Dean, Cas fled in the opposite direction. He could not lead the Leviathan back to the human. Dean would surely die if he did.

It seemed that even in Purgatory, Castiel did not require sleep, for he was not tired when he finally landed safely, finding that he had lost his pursuers, but he was weary. Never in all his thousands of years had Castiel fled so far and so fast as then. He had not even known it was possible for his wings to ache the way they did now.

Keeping his Grace wrapped tight around him, trying to make it as small as he could, hoping he attracted less attention that way, Castiel approached a stream and knelt. The water was clear, as pure as possible in a place as wrought with sin as Purgatory. Though Castiel did not need to do so, he cupped his hands and drank slowly, savouring the icy chill that the liquid brought to his sore body. How strange, that he should keep the form of his vessel even here, though both he and Dean (and the thought turned the pleasant chills painful) were technically dead once again.

Castiel stayed where he was for several hours, straining his senses as far as he dared with his Grace as much under lockdown as was possible. Once, an unwary werewolf soul wandered too close, mesmerised by the shine of the seraph's presence, but Castiel sent him into oblivion without any difficulty.

Soon after that, he thought he felt a flicker of darkness on the fringe of his senses. He could see nothing, hear nothing, but the discomfort touched him, and he tasted a bitter flavour not unlike gasoline on his tongue.

Castiel couldn't be sure that he had truly sensed a Leviathan, but he daren't take the risk. Unfurling his wings in the span of a heartbeat, he flapped and was gone from the stream, fleeing even the possibility. Eventually, he reasoned, he'd have to let one of them find him. The alternative was that they give up and begin to hunt Dean, and Cas couldn't stand that. At least the angel had a chance of outrunning them. If they decided to chase the human, then Dean was as good as eaten.

The area in which Castiel appeared was not as far away from the stream as his previous flights had been, but it was still a significant change in scenery. Sheer cliffs rose to his left, a rusty brown colour, and a field of dead grass continued out to his right.

A collection of boulders lay scattered around the base of the cliff, and Castiel tripped and stumbled his way over to them, unfamiliar with the action of running. Normally, when he went anywhere in haste, he teleported, but the use of his wings was almost as bright a beacon as use of his Grace, and so he ran. The celestial being somewhat suspected that he would very quickly get used to running.

Once he was hidden in the boulders, ensuring that no soul would find him by physical sight, he allowed himself to relax just a tiny iota. Nothing was trying to kill him at that very second, and he could stand to think for a minute.

Perhaps he shouldn't have left Dean like that. Considering his departure, Castiel began to feel a little guilty. Dean didn't know why Cas had vanished without explanation. Clearly he had not been able to sense the approach of the Leviathan. He would probably be angry. And if Cas knew Dean (and he did), then the Hunter would not stop cutting his way through Purgatory until he found the angel. They might have had their problems, but Cas was the only thing that Dean knew in this place, and so Dean would search him out.

Until that day, however, Castiel resolved to keep moving, to stay ahead of the Leviathan, and to ensure that they caught his scent just often enough that they did not remember Dean.

For the rest of what passed as day, Castiel moved from place to place, never staying more than a few hours anywhere for fear of discovery. Occasionally, he would be forced to smite a vampire or a werewolf or any other monster that dared get too near, but most of the time they did not dare, and Cas did not remain long enough for them to do so.

Soon enough, the sky began to darken once again. It did nothing to erase the gloomy luminosity that lit Purgatory, but everything did seem somehow darker under that blank slate sky than it had beneath the concrete one.

Castiel did not require sleep, but he knew that the Leviathan slept sometimes, so he felt safe enough to remain longer during the mockery of the night. He had settled amidst a jungle, full of trees and swamps and the more dextrous of monster. At that moment, he was seated halfway up a large tree, leaning against the thick trunk. All too soon, he would learn not to sit anywhere, but it was not something he yet understood.

It was then that he heard it, faint and ghostly in his ears; but even though Dean was beyond his senses, a prayer was a prayer no matter where uttered, and Castiel had no choice but to listen.

Uh, Dear Castiel, I have no idea where you are, but some company would be really nice right about now. I, uh, I got torn up pretty good by those gorilla wolf bastards, so, heh, you think you could zap on over and give me a hand, buddy?

There was no goodbye, no signing off as most people did when they prayed. For most people, praying was a devout experience, something they did out of love and faith. But as ever, with Dean, he viewed prayer as nothing more than a mode of communication; a way to contact Castiel when he was beyond all other means.

When he had first learned the expression, Castiel had been confused by the metaphor 'my insides twisted'. He understood that it was designed to convey panic, or anxiety, but it had never seemed to quite connect with the words. Now, he thought he knew why. Both emotions flared in his chest, upon hearing that Dean had had trouble with the souls, that he was injured, and it did almost feel as if the flesh in which he still mysteriously resided twisted upon itself.

How strange it was to him, even after all this time, that emotion could warp physical sensation so.

But Cas did not dare answer the prayer, and after a minute the gentle tug that told him where it came from faded. If he complied with Dean's request, then the human would surely die.

The Leviathan were not quite as many as they had believed. Purgatory was unimaginably vast, even for the angel's mind. But being near Dean was a risk. No matter how small, it was too much of a risk for Castiel to take, when the spoils was Dean's life.

And for weeks, Castiel continued in this manner. Flying all around Purgatory, until his wings were constantly paining him, never staying in one place for more than a few hours. The nights were better, because the Leviathan were less active, and the only things foolish enough to approach him were easily smote. But they were worse, in a way, because every night, without fail, Dean would pray to him, and Cas would fight the urge to respond. At the very least, Castiel comforted himself with the fact that every prayer was another day that Dean had survived; and the Hunter was practical enough that he always informed Cas of his condition.

It was, perhaps, unusually considerate of the man, but Castiel took the news gratefully. Though he knew Dean must worry about him in return, at least he would know should something happen. And without the ability to fly, Dean would always be relatively easy to find, given that Cas always knew where he was at nights. The human couldn't travel that far in a single day.

As it turned out, keeping the Leviathan interested in him proved far easier than Castiel had originally assumed. They were far more skilled at finding him than that first night would have suggested, and by now every single one of them was on the hunt for the seraph.

For weeks more he continued like this. Sleep he did not need, but even angels were habituated to periods of rest, and Castiel knew that eventually he would slip up. It was draining, constantly being on the lookout, continuously keeping his Grace under tight reign. Already, slivers of his power escaped his control, and they were practically guaranteed to bring Leviathan running. Eventually, he would need to stop, to let his Grace roam outwards and his senses roam inwards, and then he would be truly exposed. As of yet, Castiel had not thought of a good solution to that problem.

But all in good time, he supposed. Soon enough, he would have to fly. For now, he settled back against his heels (as relaxed as he could be, still poised for flight), and awaited Dean's nightly prayer.