Cas would almost have preferred Dean was never pushed so close to human again. As hard as the past week had been, watching him suffer like this was far worse.

He returned from the kitchen with a cup of water and a mug of soup (Sam's suggestion) and set them in front of Dean where he sat on the couch, wrapped in a blanket.

Dean didn't seem to notice, his gaze far off in the distance. Cas studied him a little closer. He had developed a fever in the middle of the night that had yet to break, the speckled sweat on his brow complimenting the shaking that never quite seemed to ease up. It was clear he was in pain, but the true agony still seemed to build and fade in waves. He had hoped it would settle, but there seemed to be no set pattern to when it would strike.

"You should eat." Cas prompted gently. "I think you have to now."

"You have to now." Dean replied absently, his eyes still not focused. "You've needed to since you got here."

Cas fell quiet, considering that for a moment. Dean had no reason to lie now, he had been more or less himself since he woke up. He wasn't sure what to make of it. Still, he stood and poured a second mug, coming to sit across from Dean without protest. It wasn't worth arguing, especially if it offered even some small comfort.

Dean glanced up at him, a flash of… relief?... crossing his face. He finally reached down, picking up his own, though he didn't move to drink it just yet.

Castiel sighed, fighting the urge to ask Dean how he was doing again. It wouldn't help, and it was obvious anyway.

Dean was lost in his thoughts for a few more minutes, and the angel jumped slightly when he broke the silence. "Cain said…" He trailed off for a minute, and Cas wasn't sure he'd continue. Dean took a deeper breath. "He said I was like him."

"You're not." Cas interrupted firmly.

Dean ignored him. "He said it was only a matter of time before I lost control… before I killed you and Sam, and anyone else I ever cared about."

"You won't."

"I don't care much about Sam." He said blankly. "I mean, when I'm like that I don't… sometimes it sparks up, but… It's like it's hidden behind a wall. My own baby brother and I couldn't give a shit."

"You do care, at least a little. When we were curing you, there were so many ways you could have hurt Sam… you didn't."

"Yeah." Dean whispered, his voice distant. He gave a shuddering sigh. "The other day… when I…" His breath caught in his throat. "I was going to kill you… I couldn't stop, I would have killed you if you-"

"You didn't."

"Only because you got away."

Cas closed his eyes. "We'll get through this."

"No… Cas, I don't think I will."

"Sam and Kevin and-"

"The mark, yeah I know. They have theories. But if they fail, what then?" Dean asked, his eyes suddenly sharp and alert, and almost begging Cas.

"Then we help you control it."

Dean's face morphed into a pained expression. "Cain controlled it for centuries. One fight and it sparked a genocide."

"Colette died." Cas said, voice barely above a whisper. "I'll be at your side the entire way."

Dean frowned, staring at him, his spine shuddering slightly at the conviction in Cas' voice. "If someone killed you, if I kill you, I'd kill every last person on the planet." He said evenly.

"Then I suppose I will just have to not die." the angel replied.

"Cas-"

"You are stronger than Cain."

"I'm really not."

"You really are."

Dean closed his eyes. "It only took me thirty years to break."

"I wasn't there. I won't let you break this time."

Dean looked away. He set the mug back on the table, his stomach turning even at the thought of eating right now.

Cas sighed. "And frankly, you don't have a choice." He said at last. "Even if you wanted to die, you couldn't." He watched Dean open his mouth and cut him off before he could begin. "I don't care what you did to Abaddon."

"It was a solution."

"Fine. I promise you if you start committing genocide I will personally separate your head from your body and guard it until the end of time itself."

Dean gave a weak smile in spite of himself. "How sweet."

Cas relaxed slightly, leaning back in the newly returned chair, the conversation leaving him drained. "Of course, I'd rather we make sure it doesn't come to that." He muttered.

The hunter rolled his eyes. "Yeah, yeah."

Cas looked away, a small smile at the exchange.

"How long do you figure I got?" Dean asked.

Cas chose to feign ignorance which, by the hunter's glare, didn't work. "Before what?"

"Before I'm not myself anymore."

Cas sighed. "I am not sure. I didn't even think this would be a side effect of the withdrawals."

"Will you know?"

"It is easy to tell."

"Can you see it?"

Cas frowned. "See what?"

"My true face?"

"Yes." Cas said simply. "And your demonic face as well." He purposefully misinterpreted Dean's question. "But it isn't like other demons."

"I don't-"

"You aren't possessing someone. You never have been, I don't think you even can. You were made a demon. Your face is your own." He shook his head. "But yes. I can see that distortion."

"This is me."

"Perhaps." Cas relented. He gave a half shrug.

Dean grunted, pulling the blanket a little closer and resuming his stare into nothing.

Cas let him sit for now, turning his attention back to a book he was only pretending to read.

Dean only let the silence continue for another few minutes. "Do angel wings really have feathers?"

Cas frowned, looking up.

Dean continued. "Like actual… feather feathers?"

"Yes and no…" Cas said slowly. "Sometimes, in certain…" he froze, searching English for how to properly describe what he meant. "When they are closest to manifesting in this time, and this physical state, yes. And as such can be made in-part corporeal and a feather is formed."

"And otherwise?"

"It would be easier to explain it with more math than you're willing to put up with."

Dean flopped back against the couch, dissatisfied with the incomplete answer.

Cas looked at him critically. "What is the point of all these angel and demon questions?"

"This time was genuine curiosity."

"And the others?"

Dean failed to stifle his slight amusement. "I'm literally just fucking with you."

Cas tilted his head. "What?"

"I'm just doing it to get in your head." He managed to look a little remorseful. "Sorry."

Cas rolled his eyes, but he found himself smiling in spite of himself.

"If it makes you feel better, I ruled out burning the cabin to the ground to escape."

"It doesn't, thank you." Cas replied, shaking his head.

"No problem." Dean closed his eyes, laying his head down against the pillow.

Cas thought about his next words. "We need to discuss a plan."

Dean's expression closed off. "Yeah." He said softly. "We do."

"Other than planned excursions, we should probably keep up with food preparation, as it seemed to be doing some good."

"You're kidding, right? I practically carved you up with that knife."

"We'll take extra precautions."

"What, salt around the cutting board?" He stared at Cas' sincere look. "You're serious?"

"Or I can take it behind the salt line entirely."

"Yeah, I'm sure that will work." Dean muttered.

"I don't see why it can't."

"And what happens when I take the burning hot pan and hit you over the head with it?"

"Dean, I move the logs in the fire with my hands."

"It's still a pan."

Cas let his gaze wander over to the kitchen. "As you pointed out yesterday, anything in this cabin can be a weapon."

"All the more reason to-"

"I am not leaving." Cas repeated, his voice dropping with unmistakable warning.

The hunter froze in place, looking up at him. He reluctantly decided it was best not to argue.

Cas thought for a moment. "I could ask for more movies for your laptop. Since we cannot access the internet here."

"Yeah, fine." Dean muttered. He looked for a second like he had more to say, but he was choked off by the sharp return of searing pain. "Cas-" He gasped before his breath ceased entirely, body pulling rigid, so tight his joints nearly dislocated themselves all at once. He clenched his fist, curling into himself as much as possible before he lost control entirely.

Cas jumped up, reaching him just in time to catch Dean as he pitched from the couch. Late into the night the pain had started to build to the point of seizures. Cas gently guided him from the furniture, waiting for the fit to pass before pulling Dean back up to lean against him as soon as it did.

Dean's hand snapped out and grabbed Cas' forearm, bracing himself against the remaining agony.

Cas wrapped his other arm tightly across Dean's chest, helping to hold him steady until his body began to finally relax.

Dean finally managed to force cramped fingers to loosen, letting Cas slip free. He let his head fall back against him, allowing the angel to take his weight entirely. He reached up a shaking hand, roughly wiping at the deep crimson dripping sluggishly from his nose.

Cas gently ran his fingers back and forth on Dean's chest. "Just breathe."

Dean coughed. "Easy… for you to say."

Cas felt somewhat reassured by the response. "Let's get up on the couch." Cas shifted, looping his arms under Dean's, helping him back up and onto the cushions. He touched his hand to Dean's forehead for a second, frowning at the growing heat. "Take this flannel off." He instructed, reaching out and helping to free him from the outer shirt.

Dean gave a weak wry smile in spite of his exhaustion. "Mrs. Robinson, you're trying to seduce me."

Cas tilted his head, confused. "I-"

"It's from a…never mind." He dragged up the energy to roll his eyes, letting it go. He didn't ask permission before he pushed Cas down to the back of the couch and laid himself against his chest. "You would think I'd be human enough to pass out."

Cas flashed a look of sympathy towards him. "They're getting a little longer apart."

"Could have fooled me." He winced. It felt like every time he got his breath back it was knocked out again.

Cas shifted, helping to settle him a little closer.

Dean absently brushed his fingers against the now red skin of Cas' arm where he had grabbed it just moments ago. "That's going to bruise."

"It's okay." Cas tried to reassure him. "And they are slowing."

"Great. So then I get to become more and more a demon instead."

Cas didn't say anything, knowing nothing was going to put his mind at ease. Especially when he wasn't wrong.

"Your bedside manner sucks."

"I'll take that under consideration."

Dean relaxed slightly and he allowed himself to sink just a little further beside him. "See that you do." He continued, taking the comfort for what it was. "Is this okay?" He checked in, ready to move if asked.

"Yes." Very much so.

Dean let out a soft hum as Cas resumed absently running his hand back and forth across his chest. "So they didn't find anything else yet?"

"They were a little distracted by Cain."

"Mmh." Dean agreed, letting his gaze wander over to the fire. "Do you actually think they'll figure it out?"

Cas hesitated before taking a deep breath. "Yes."

"But?"

"I do not know how soon. It is encouraging that they have found anything about the mark in the tablets."

Dean nodded slowly. "But you think they will figure it out."

"I do." Cas said softly.

The hunter shuddered slightly, turning slightly against the chill of the cabin.

Cas reached down, grabbing his flannel from the arm of the couch and draping it over him.

"Thought we had to keep the fever down."

"A compromise." Cas offered.

"Thanks."

Cas readjusted slightly, taking a moment to think. "What else did Cain say?"

"He offered to join up with me. Together we could have broken the wards, worked with each other."

"Why didn't you?"

"I really wanted to stick that blade through his heart."

Cas winced. "Is that the only reason?"

"Yes." Dean hesitated. "I'm not sure." He frowned. "I got angry when he said it… when he said I'd lose control and… I didn't want him to be right." He hesitated. "But I don't know if it was for the right reasons."

The hand on his chest stilled for a moment. "Maybe it doesn't really matter what the reasons were."

"Yeah, I guess."

"It's over now, either way."

"Yeah…" Dean mumbled. He turned his head , feeling the stiff fabric of Cas' overcoat on his cheek.

Castiel dropped his voice. "I missed this." He admitted.

"We can't… what happened with the salt… you can't…" Dean tried to get his meaning across, his voice pained. "You can't let your guard down like that again."

"I know."

"It's not safe." Dean shook his head. "In the bedroom. Two salt lines. Away from me." he stressed.

"I will."

Dean let out his breath.

"It's okay Dean." He adjusted his hold around the hunter. "We'll be okay."

The hunter paused before nodding, letting his body relax again. "Yeah… Okay."

.

"We got it!"

Sam snapped his head up off the book he hadn't meant to nod off on top of. "What?"

Kevin threw a notebook down on the table, his wide grin rivaled only by Charlie's.

The hunter picked it up, scanning over the mess of writing and translations. "Break it down for me."

Charlie sank down into the chair across from him. "A real bonafide lead in the removal of a celestial brand." She held out her hand and took the notebook back. "That book, the one in Pumpernickel-"

"Pumpokol." Kevin corrected.

"Yeah sure, whatever. The deader than dead language. We found the spell that unbound Hera."

"The Greek goddess." Sam followed.

Charlie nodded. "Turns out she was cursed by Zeus himself. Pretty powerful stuff."

"And the Men of Letters managed to break it?"

Kevin leaned back against the other table. "Completely."

"But this isn't just any curse…"

"No." Charlie agreed. "It's a demonic, angelic, god brand."

"Or key." Sam reminded her of their awkward translation.

"We're running with brand." She turned the page, revealing even more scribbles, this time in Latin. "In that book on demonic curses, we found one said to be able to free a demon from the bindings of the pit."

"What does that mean?"

Kevin took the notebook. "Think of hell like the ultimate shackle. Demons draw their power from there, but it's also still a prison. When they're exorcised they end up right back there, and it weakens them every time."

Sam nodded, finally catching up. "So there is a spell that severs the demon from hell itself." He frowned. "Wouldn't that cut off their power?"

"Not necessarily. But it would change it." Kevin conceded.

"So what does this all add up to?"

Charlie looked down. "We already know the archangel warding. We think if we can mix the power in those sigils into the spell work used to unbind Hera and the ones separating a demon from hell… we think the combination might be enough to interrupt the mark's power."

Kevin closed the notebook. "And we think that will be enough to rip it off."

Charlie winced. "Key word being think."

Sam shook his head. "No, no. This is good. This is something." He looked between them. "What now?"

"Now is the hard part. We have no idea how to actually combine them."

The hunter frowned, heart sinking as he realized the obvious. He closed his eyes. "Crowley-?"

"Yeah, that's what we were thinking. Of course we had been hoping to avoid using him this much."

Sam didn't move for a moment. "Well…" He sighed. "We didn't keep him locked up here for nothing."

.

"This, I'm afraid, is well beyond me." Crowley shattered their hopes as quickly as they presented the pages to him.

"You have to know something." Sam insisted, his tone tipping more hostile.

"Spellwork never was my forte." The demon dismissed, putting the notebook on the table and pushing it away. "Magic like that is serious stuff. Not just anyone can do it."

"You have connections all over Hell and Earth." Sam snapped. "You know someone who can get the job done. Someone who can decipher and build a spell like that."

Crowley froze, expression falling. "Bollocks."

"What?" Sam demanded.

"You need a powerful witch, one who studied the magicks of old for centuries."

"Skip to the part where you tell me who they are."

"I know of only one witch who could do the job."

"Spit it out, Crowley."

"My mother."