Castiel hears something and stops in his tracks. He waits, listens. Nothing.
He takes a step to continue on his way, and realizes that Dean isn't with him anymore.
Castiel turns, but there's no sign of his friend anywhere; only dense, cold fog.
He surpresses the urge to call out, that would only give away both him and Dean to the monsters. Instead, he watches and listens.
He sees dark shapes through the fog, hears the sounds of a scuffle, and runs towards it. He doesn't fly - this place drains him, as Eve did. Save it for fighting, Cas, Dean had said, and at the time Castiel thought it was a prudent suggestion, but now Dean is fighting things, and Castiel isn't there to help him, and I can't lose him,not now, not like this.
Castiel reaches the spot where he saw the shapes, but no one is there.
"Dean!" he yells, caution giving way to fear. "Dean!"
He hears shouts and growls, but the fog disorients him, Castiel can't tell where the noises are coming from. He spins around, but it's all just pressing, suffocating whiteness, broken only by the dark pillars of tree trunks. Then he sees shadows, grappling, piling on one another. He spreads his wings, and he's there.
There's creatures all around him now, attacking one another, attacking Dean, but the fog is so thick that Castiel can't distinguish one figure from another. "Dean!" he calls again, and he thinks he hears an answering shout, but it's lost in the yelps and snarls of the monsters.
A thing with fangs and claws leaps towards him. Castiel steps out of the way, grabs the thing by the throat, and slams it into the ground. A flash of grace lights up it's face, and the soul dissolves, to re-materialize elsewhere. Nothing can die here.
Except for Dean.
"Dean!" Castiel shouts one more time. "Shut your eyes!"
It takes every ounce of power that Castiel has, but he lights up the forest, burns away the monsters, and burns away the fog.
Suddenly, supporting the weight of his vessel feels like far too much effort. Castiel collapses on the ground. He feels blood collecting in his throat.
"Cas?" he hears faintly, as if through water.
Dean Winchester's face swims into focus. He's scratched up, but in one piece. Castiel attempts to smile, but doesn't think he's very successful.
"Jesus, Cas," Dean says, out of breath and edgy. He kneels next to Castiel, trying to asses the angel's condition. "Let's never do that again."
Castiel's pretty sure he manages a smile this time. "Agreed."