A/N: Because I just watched the finale, and it had to be written. And because the title practically lent itself to the situation. And it turned out a bit gloomier than intended, but there isn't another fitting way to end it.
If nothing else, Dean is pretty sure he'll go down in history for being the only person ever to get stuck in purgatory with a crazy angel, while they're still alive (at least, they are for now).
He's alone at first. Not literally, at first, because Cas has the courtesy to wait until he's awake to pull a disappearing act, but for the first hour/day/week. He can't really keep track of time here, since he's always tired and always hungry and always running. And the sun never rises and the skies never change, if the endless expanse of black above them could ever qualify as a sky.
It doesn't take him long to start running. He has no weapons, no way to fight, no idea what he'd even be fighting. But the hissing, snarling, circling monsters with red eyes don't seem to give him great odds, even if he could see properly. Which he can't, really, but when he thinks about it (which he tries not to) he shouldn't be able to see at all, because there's no light source save for the glowing red eyes that are everywhere.
He's running from those same eyes, panting for breath and as desperate as ever when something, someone grabs his arm. He instinctively pulls away, ready to fight it before seeing that it is, in fact, Castiel. Sitting against a tree, staring at some point out into the blackness.
"Cas." He doesn't ask the angel why he left, before. He's not even sure Cas could answer. The angel's still not all there. But he's glad that someone is there with him, besides the monsters.
"Dean." Castiel responds, still not making eye contact, but acknowledging his presence. "There aren't any monkeys here."
He's caught off guard, but he should have expected it. Cas's brain doesn't seem to be great at prioritizing.
"No, there aren't," he agrees, "But Cas, we gotta get out of here. They'll be coming."
"They're everywhere," is the response after a long pause, so long Dean almost thinks the angel didn't hear him. "It doesn't matter if we leave."
"But they know we're here, so we've gotta keep moving."
"I think it's a good thing."
"What?" he catches Dean off guard again.
"That there are no monkeys. They'd just get eaten." He unconsciously adjusts the trench coat he's still wearing and turns towards Dean, looking up.
"Dude, we really gotta go." Dean shuffles anxiously, glancing around. The red eyes are getting closer.
"Of course," Castiel responds this time, and Dean reaches down a hand to help him up. He takes it, and Dean suddenly feels as though he's been punched in the gut.
He cast about, gasping, to realize that Cas is now standing up and they're beside a different tree.
"Dude, you can't do that!" Dean reacts as soon as he catches his breath.
"You wanted to move," and now he's confused, his head tilted in his typical quizzical expression.
"Yeah, like, move. Run. Not angel-teleport."
"Oh." Castiel stands there a minute. "Sorry."
They're still alive days/weeks/months later, when they realize they can't keep running forever and fight off their first thing. Castiel appears to have given up on his no-fighting resolution (admittedly, these are extenuating circumstances) since he pulls it off Dean and brutally kills it with a dead branch.
Dean picks himself off the ground and just looks at Cas. Cas just picks up the branch and keeps walking.
It's times like those when he's glad to have the angel with him, those periods of lucidity when Cas is back to being a warrior, a soldier, and a friend. Then there are times when it seems like the angel has so many screws loose it might be a mercy to kill him.
When he isn't lucid, he alternates between apathetic, panicked and completely out there. Apathetic is when he sits down and decides he doesn't care that he's going to get ripped to shreds and Dean has to drag him along to prevent him from turning into something's lunch. When he panics, it's all Dean can do to hang on while the angel teleports wildly and flails at the shadows.
Then there's the times when he's less sure that Cas has completely lost it and more sure that's he's just a little mixed up. Like when they are attacked by strange little primates with long, hooked yellow nails and bright red eyes. The claws seem filthy, and they're plenty scratched up by the time the last one has been beat to death. Ordinarily, Dean would be worried about some sort of demon pestilence, but he's pretty sure it couldn't get much worse than it is.
"Dean?" Cas asks, as they stand around the hideous corpses and catch their breath. "They look like monkeys. I didn't think there would be monkeys here. Just tigers."
"Tigers?" Because they've ran into a heck of a lot of things, some of it recognizable, some of it so twisted that it's beyond even guessing what it once was, but he's pretty sure tigers weren't part of it.
He seems pretty checked out at the moment, staring up at the sky (Dean's decided it isn't worth coming up with another name for it) with his hands in his pockets. "Tiger, tiger, burning bright, in the forests of the night."
"Ah." The rhyme strikes a faint chord, and he knows he's heard it before, and obviously Cas has too. "In the forests of the night."
Time passes, Dean has no idea how much. His sleep is always brief, fitful, awoken by Cas and teleported without warning. Then they keep moving, desperate and fighting. He's hungry, but he doesn't seem to need to eat, which is some small mercy given as there doesn't seem to be any food. He supposes all the monsters here just eat each other.
The panic goes away first. He isn't sure how long it is since the last time Cas started trying to run away, spooked by something, but he notices it stops. The apathy next; Cas is as eager as he is to survive, to move.
Then one night, and there's a mutated version of a Wendigo and they're fighting it, and the angel grapples with it while Dean searches desperately for some sort of fire. He ends up attacking it just to keep it from killing Cas, and the angel turns and is holding a burning branch and then the monster is burning at their feet.
He doesn't say anything about monkeys or insects or tigers. He just puts out the flames when the thing is nearly ash.
"Let's keep going," Castiel says, and just like that Dean knows he's back.
"Yeah, sure."
They don't talk about it. They don't need to.
Desperation eventually ensues.
They are continually battered, scraped, beaten, exhausted. Spattered in the blood of monsters and their own blood, and running. Always running.
When Dean can sleep, he drifts off instantaneously, and is always plagued by nightmares until Castiel wakes him and they're off again.
He thinks about Sam. He thinks about how to escape. He thinks about dying.
Dying. Here.
It's only a matter of time, he eventually figures. They try to move in just one direction, as if hoping to come to an end. But they can't find one, like they're caught up in a dark giant sphere and there is no way out. And Cas is limping and Dean is bleeding and there is no way out.
He figures it will happen soon. The monsters will surround them, and they'll die surrounded by red eyes and dead trees and just be another couple of corpses to litter the floor.
A couple of corpses, in the forests of the night.