A/N: I like to pretend Bobby never died and other inaccuracies.
Cas doesn't heal right away. Doesn't heal at all. Won't stop seizing periodically.
"It's eating at my grace," Cas says, when he wakes and they realize it's not going to go away. Realize they don't have a clue what it's doing or how to fix it. "Tearing it away little by little." He says it so easily. So straightforwardly. With only the barest hint of sadness in his eyes and voice—buried beneath pain.
"What'll that do to you? If it eats it all?" Sam asks because Dean can't.
"I am my grace," Cas says, and his voice jerks and his arms jerks and his eyes roll and he's seizing again.
Sam drowns himself in research. Dean just drowns.
"Can you lift your head a little?" he asks, trying to get some water into Cas because Cas is losing his grace and as far as Dean knows fluids are good for sick and dying—fluids are good.
"I'm… trying." Cas's head is twitching forward, eyes fluttering open and closed and open and he's panting way too heavily.
"Breathe, Cas." Dean runs a hand over his chest, trying to help his lungs settle into a more normal pattern. He moves his shoulder and arm up, shifting Cas's head and pulling up his own hand. "Okay. Don't worry about it, I got you." He lifts Cas's head carefully upright and tips the cup to his lips, "Just swallow this for me."
Cas gets most of it down. He falls asleep again and Dean lays him carefully back down. He heads out and finds Sam.
"I called Rowena," Sam says.
Dean's head lifts just a fraction, almost-hopeful. "Yeah?"
Sam shakes his head. "She'll keep looking."
Dean goes out to clear his head. There's dried blood outside where Cas was shot. Dean stares at it for a moment. And then he slaps himself on the head and runs back inside. He races to the library because that's where Sam is.
"They know where we live," he blurts. "We're such idiots."
Sam snaps his book closed. "They'll be missing us by now."
"Yeah, I know. They could get here any second." Dean searches his pockets. He throws the keys at Sam. "You get the car, I'll get Cas."
Dean marches to his room and packs a duffel that he throws over his shoulder, then he marches back to the angel's room and up to the bed. Cas is asleep. Dean pulls the blankets down and starts to scoot Cas closer to the edge of the bed in preparation to lift him.
Cas's eyes start fluttering, his limbs jerking like he's trying to fight.
"Just me." Dean folds Cas's arms over his chest and slides an arm beneath his back, another beneath his legs, already pulling him up.
"Dean," Cas slurs, eyes closed, head lolling against Dean's shoulder as the Winchester lifts him. His hands and breaths are shaking. "Sam okay?"
"Sam's fine."
"Okay." Cas's head goes still; limp against Dean. He's out again.
Dean tilts his head down and rests it over Cas's mop of dark hair. To keep the angel's head from rolling or flopping back. Sure. He heads out the car.
Sam is already there, throwing things into the back, looking up at Dean's footsteps. He hurries around to open the car door for him.
Dean shuffles past him, carefully arranging Cas into the backseat. He forgot a blanket.
"Is he okay?" Sam's whispering to him, voice concerned, "Didn't he wake up?"
Dean slips out of the car, patting Sam on the chest, "Just long enough to ask if Sam was okay."
Sam shakes his head, shoulders falling.
Dean sighs. He closes the door, hand lingering on the frame, "He's getting weaker fast. We've got to fix this faster."
He runs back inside and grabs a blanket. Five minutes later, they're driving away. They'll come back if they can. After Cas is fixed and they're more prepared to deal with the looming threat of—Dean has run out of insults. Screw them anyway, the Winchesters will be back.
They pull up to a motel a few hours later. They settle Cas into one of the beds and get to work.
Dean glances at his phone and realizes he's missed a call. He listens to the voice mail and then tells Sam, "Bobby called back."
"And?"
"Something about the cores of demons and angels being incompatible." His head tilts down as he glares at the book in front of him. "Violently incompatible. That's all he got."
Dean wants to keep them moving. Can't seem to settle anywhere. Sam doesn't comment on it. They pull up to another motel and Sam tilts forward and climbs out. He throws a wallet at Dean. "You get the room, I'll get Cas," he says, beating Dean to the punch for the first time in three days.
Dean is back before Sam's even gotten him.
Sam opens the back door and bends down, sliding an arm beneath Cas's back, starting to slide him out.
Cas's eyes flutter. His head lolls backward as it comes off the seat and Sam adjusts to pull it onto his shoulder. "Wha…" Cas murmurs, but his eyes don't open. His hands twitch.
"It's Sam, Cas. You're okay." Sam pulls the angel's legs out and stands.
Cas's eyelids flutter. "Sam?"
"Yeah," Sam says softly.
Cas's hands twitch, curling just slightly in the fabric of Sam's shirt. "Dean okay?"
Sam closes his eyes. "Yeah," he says, and he hides the wobble well. "Dean's okay."
"'Kay," Cas breathes. And then his eyelids still and he somehow goes even more limp.
Sam shoves the car door closed.
Dean opens the motel door and Sam moves in to place Cas carefully on the farthest bed, Dean rushing to pull the blankets back before he does.
Dean drapes the blankets over Cas.
"Dean, he barely wakes up anymore," Sam whispers. "I don't know how much time we have. We have to do something now. Maybe call another angel."
Dean shakes his head. "Cas doesn't know the antidote. I don't see why other angels would."
"Maybe they could heal him."
"Who?" Dean's head twists up. "They hate him."
"We have to do something, Dean."
"I know," Dean growls, shoulders falling. "Dammit, I know."
"It was demon blood, right? So let's ask a demon."
Dean picks at his teeth with his tongue and shakes his head. "Crowley doesn't know. He's working on it. Rowena's working. Bobby's working. Everyone's… we'll get something. We will. We have to."
"Dean," Sam murmurs, and pulls him away a little. "He's dying."
Dean shakes his head harder. "He's just weak. He could pull through."
Sam sighs but doesn't argue. "We tried holy water…"
Dean nods. "Yeah."
"Devil's trap wouldn't do crap. Salt wouldn't do crap."
Dean rubs his hand over his mouth and stares at the floor.
"All we know is how to fight things. Not cure them."
Cas starts shaking on the bed. Seizing weakly. Dean runs over to brace him, Sam just behind. "You're okay. You're okay. You're okay." Tears roll down Cas's face, though he doesn't wake. "You'll be okay." Dean keeps murmuring even though both siblings doubt Cas is hearing him.
When it's over, Sam straightens and murmurs, "Maybe the men of letters know."
Dean sets his jaw hard and fast. "They did this to him."
"So they can undo it. We'll capture one… we… we'll storm the place. One of your stupid ideas, huh? Come on." Sam's throat bobs. "Come on."
Dean nods slowly. He rubs his forehead. "Right. Call Bobby. Have him meet us some place, we'll leave Cas with him and then...we'll figure somethin' out."
"Right."
Bobby meets them halfway the next day. He opens the motel door and they walk in, Sam carrying Cas. Bobby points him to the bed by the wall. Sam lays Cas down, hands lingering. "Um… you just…" Sam fiddles with the blankets, looking at Cas and not Bobby. "You need to make sure he doesn't roll off the bed or anything, when he seizes, you know? But he's been pretty weak, so he's not likely to do that again. Uh… we should probably move the bed a little farther from the wall so he doesn't hit it. And if you can get some water into him..." Sam rubs at his forehead, then adjusts the blankets over Cas, pulling them a little higher, smoothing them down. "But he… he hasn't woken today, so you might need to do an iv line."
"Sam. I got 'im. You go save him."
"Yeah." Sam's voice is ragged.
Dean sighs. "Just keep him alive, Bobby. We'll be quick as we can."
"Go, you idjits."
"Sam," Dean calls.
"Bye, Cas. We'll be right back. Bobby'll watch over you."