I ficced about what might happen later in Supernatural s8
Dean sat on the dusty table in what he still thought of as Rufus’s kitchen, ticking things off on his fingers. "Well, we've got the half a demon Tablet, and Crowley's got the other half. Don't know what happened to the Leviathan Tablet while I was gone - Sam probably fed it to a dog or something. Then-" a thought stuck him, and he tested it out loud. "Hey, Cas, is there an angel Tablet? We've got Hell and Purgatory, so why not-"
Cas looked up from his newspaper. Suddenly, without seeming to move (as usual,) he was standing directly in front of Dean, deadly serious.
"You can't know about that," he said. Each word seemed forced violently out, echoing with conviction.
"Cas?" asked the hunter, scrambling backwards on the table. But the angel caught his wrist in a grip like steel, and he could only lean so far back without getting his arm ripped off.
Cas's head jerked sideways, mouth opening and closing like he was about to argue with someone. A thin rivulet of blood leaked out of one eye. "I'm sorry--"
There was a blade in his hand and he raised it, aiming unsteadily at Dean’s heart
"Cas!" shouted Dean. He kicked his friend in the wherever his feet could reach, but the angel didn't react.
"You- I- must-" Cas was having some sort of vicious fight inside his head. The knifepoint wavered about.
Then something just went blank in those big, wide, blue eyes, and the angel’s blade clattered as Cas fell to the floor, blood trickling down his pale cheek in vivid red tracks.
Castiel woke up in a bed. It was a sufficiently unusual situation that it took him a moment to understand where he was, and why he was covered in soft linens, but the situation became much clearer when he opened his eyes and saw the slightly musty comforter and ratty floral-patterned sheets. He was in the bedroom that used to belong to the hunter Rufus, he believed, in the cabin of the same. It was nearly dusk
Dean was in the bedroom as well, slumped in a chair near the foot of the bed. It didn’t look like a terribly comfortable chair, but the hunter was fast asleep, snoring faintly (he didn’t usually snore, Castiel knew, but it was clear that the tilted position of his head was impeding the flow of air to his nasal passages.) The angel took a moment to appreciate the ruffling effect of the chair’s backing on his hunter’s honey-colored hair, the way the dust motes swirled around his face in the dying light of the sun, the slight rise and fall of his chest with every breath. Dean was always very peaceful when he was asleep.
But he did, Castiel reminded himself, object to being observed in such a state. So he announced his awakening, in a voice gravelly from lack of use. “Dean.”
The hunter’s head jerked up. Castiel wondered how long he’d been sitting there. "Cas. You're up." An expression of joy, of relief, flitted across his face, replaced so quickly by the usual worry.
"What happened?" asked Castiel, wincing as he struggled to sit up. There was a pain in his head, throbbing and stabbing at the same time, and however he willed it would not go away.
Dean sprang up, coming automatically to help, but then checked his movement and didn't approach the bed. For the first time, Castiel noticed the sweet smell of holy oil, poured in a neat circle around the bed. And that Dean, not himself, was holding his blade.
“You...passed out,” said Dean cautiously. “Do you remember anything?”
Castiel shifted through his memory and found that he did. Dean had been thinking aloud, as he was wont to do, and asked about the possibility of a Tablet about angels. And suddenly Castiel had known, known, (or possibly remembered? but his mind skipped over that, and he let it) that there was such a Tablet, and it must be kept secret at all costs because who knew what it could do to Heaven, to his own siblings. The secret had to be kept, no matter who had to die - whether it be he, Castiel, or any other angel, or even Dean. Dean was one who might use the Tablet for some dark, human purpose. Dean had to die. He’d known that in an instant. He knew that.
And suddenly Castiel was standing on the edge of the circle, leaning forward with terrible intent. But he couldn’t step over the line of fire that Dean has just lit.
"Okay, Cas!" shouted Dean. He was standing now, Castiel's blade held at the ready, with all the decades of hunting experience behind it. "What is up with you? I know it’s not Crowley again, because you wouldn’t, I know that. But what the hell is going on here?"
Castiel stumbled back from the flames. He wanted to sit on the bed and hold his aching head, or possibly just sleep some more, but he couldn’t. He had a mission, a mission he didn’t want that absolutely had to be completed.
"I-" he croaked, but how could he explain the certitude that filled him from wingtip to wingtip? Except for the small voice screaming in the back of his brain that this was all wrong. Is it the voice of doubt? Is it the voice of reason? Is it some strange leftover from the cocktail of insanity he took from Sam not two years ago?
“Let me out,” he said firmly. “I am fine, now.”
But Dean must have heard the lie in his voice, because he did no such thing. “Not until you’re done being homicidal.” He flipped Castiel’s blade into the air and caught it, again and again, a nervous habit. The angel watched it flashing in the dim light and considered the effort it would take to simply influence with spin so that it plunged into Dean’s chest. He could do that through the circle of holy fire, at least, though it might take more power than he could muster at this moment, through the blinding pain in his skull.
“Is this about the Angel Tablet?”
Castiel closed his eyes and put his hands over his ears, trying to just block out the world. “No,” he lied. “There is no such thing.” But the world was still there and so was Dean, knowing things he shouldn’t know
“Cas?” asked Dean, and despite everything his voice was filled with concern.
Castiel lay back down, burying his head in the old pillows. They smelled of goose feathers and he concentrated on that, the implied memory of flight, of neatly ordered Vs, of honking families soaring high on the wind from autumn chill to spring’s awakening warmth.
“Why don’t you get some more sleep,” suggested Dean. “I’ll go some research. Whatever’s up with you, Cas, we’re gonna beat it. Don’t worry.”
The hunter backed out of the room, leaving the door open and the circle of holy fire burning, and Castiel continued to try to think about geese. Geese were simple. He could just stay here and bide his time until Dean trusted him again and put out the fire, and then... Until then, he would wait. No matter how long it took. So long as he was in here, Dean was safe.