Dear Readers: This story takes place after the events of "Executioner's Song," but will from there on be AU. As a warning, this story will deal with some sensitive material and graphic descriptions that some folks might find hard to stomach, so please take that into consideration. However, I will do my best to make chapters with M-rated content optional, so that readers can skip them, if they'd like to, and still enjoy the story with a T-rating.

I hope you enjoy!

Servant of Heaven, Son of Cain

Chapter One

Sam had asked him to stay.

Hands in his coat pockets, Castiel paced the bunker's long, grey halls.

He was relieved, actually. It was a good excuse. With Cain dead and the blade hidden, Castiel should have been searching for some way to cure Dean of the mark. If Sam hadn't asked him to help keep watch, he would have torn himself away to do just that, despite the worry he shared with Dean's little brother.

As he roamed, the light bulbs above Castiel's head sputtered and browned in their tin pan shades. Wherever he went, the eerie buzz-pop of disrupted electronics followed. It had been while, he realized, since he'd lost control of himself like this. With great effort, pulled himself inward, condensing his energy into a tiny thrumming orb. It wouldn't do either Winchester any good if they noticed how upset he was.

Castiel made pass after pass through the bunker's many corridors, finally seeing Sam off to bed around one-thirty in the morning. The younger Winchester rubbed his neck as he climbed the stairs out of the great room, commenting ruefully, "Nothing good happens after 2 a.m. anyway."

Castiel watched him go, blinked, and then turned away. He had no words of comfort to offer.

With Sam in his quarters, the angel made his way quietly back the way he'd come, going door to door until he came to the one with Dean behind it. With hardly a sound, he passed into the room, reappearing with a flicker at the end of Dean's bed. Solemn as stone, he looked down at his friend.

A single lamp burned in a sconce above the bed, casting long shadows over Dean's twitching frame. He was asleep, collapsed in a restless mess across the bedcovers, looking like someone had tossed him there. Castiel worried at his pale skin and drawn features. Even asleep, Dean looked exhausted. The angel's frown deepened.

Despite the dark, the jawbone burn on Dean's arm stood out, hot and angry-looking. Its red power hissed and spit in a tone Castiel suspected only he and its bearer could hear. The thought of all that para-human rage weighing on Dean left him deeply unsettled. They had all seen its effect—Sam, Crowley, even Cain himself—but he wagered that of all of them, he was the one who felt that evil most strongly. The mark was, after all, an angelic brand, bastardized and ancient. Though he'd never mention it, the aftertaste of Lucifer's hatred soured Dean's every exhale, filling the air with a scent that chilled Castiel to his most constituent parts.

Shivering even in his vessel, the angel pulled a wood stool to the corner of the room and sat there, elbows on his knees, hands knitted together. Given that Dean wasn't particularly comfortable with being watched while he slept, Castiel made it so he was just outside the field of human perception. If Dean awoke, he would still sense a watchful presence somewhere in the room, but if he looked to Castiel's corner, he'd see nothing there. This was the angel's usual strategy when it came to playing keeper of his charge. It was common for him to watch over Dean, but the young man didn't appreciate it being so obvious. It was creepy, he said, and after many reminders about privacy and personal space, Castiel had finally relented. Sort of. While not quite as hard-headed as Dean, the angel had his own stubborn streak. He refused to leave Dean unattended, but arranged it so no one looking in could ever tell he was there. This seemed to sooth Dean's pride, and so it went on, never mentioned.

Lately, though, it had been different. Usually, Dean rested easy while Castiel kept watch, but since the mark, it was almost as if Dean could smell the remnants of heaven on the angel as sharply as Castiel could smell sulfur on demons. Now when Castiel came to watch over him, Dean often stirred awake, sitting up in bed and scanning the room. It unnerved Castiel to see those green eyes pan back and forth until they settled on a space very near his chosen post. He knew Dean couldn't actually see him, but though the hunter never said anything, it was obvious he knew the angel was near. Castiel's only reassuring thought was that Dean never asked him to leave.

Tonight was no different. Castiel stiffened slightly in his seat when Dean suddenly growled against his pillow, body growing taught as he awoke. Slowly, the hunter rolled onto his elbow, bringing a hand across his eyes and massaging his temples. He lay that way for a long moment before dropping his arm in defeat. He looked terrible. With a fogged expression, he stared down at the mark, looking unsurprised that it was still there, but obviously wishing it wasn't. Covering it with a hand, he sighed.

"For christ's sake, Cas, I don't know why you bother hiding anymore. I know you're there."

There weren't many things capable of startling Castiel, but Dean's remark took him by surprise. He blinked, alarmed to see Dean's sunken eyes slide over to where he was sitting. Without coming into view, the angel stood and asked, "Can . . . can you see me?"

Dean swung his legs of the side of the bed. Scrubbing his face with his hands, he blew a heavy breath, "No."

Castiel allowed himself to manifest.

"How did you know I was here?"

Dean scratched his neck and squinted at the wall, mouth pressed into a line.

"Pretty sure I always do, now," he said. He gave the angel a sideways look that Castiel refused to return. Instead, his gaze drifted around the room as he paced absently, prodding at the various weapons Dean had on display.

"I'm surprised," he said while examining a knife, "that you never mentioned it."

Castiel was behind Dean, now, and stared at the back of his head. The hunter shrugged, "Yeah, well."

He didn't continue.

Slowly, Castiel set the knife back in its place and crossed to friend, taking a seat beside him. Without a word, he reached across and took Dean's arm in his hands, examining the mark with the same gingerly attention he had given Dean's other weapons. The angel looked hard at the mark while its bearer looked hard at the floor, the lower half of his face twisted into a rueful smile.

"Glare at it all you want, Cas, I don't think the thing's gonna be scared off by dirty looks."

Castiel stared at Dean.

"This is not a joking matter."

Dean chuckled and sat up to argue, but stopped when he saw the look on the angel's face. There was deep worry there, a dark anxiety that made his gaze heavy and unavoidable. Castiel tried to contain it, but it was useless. Suddenly, the bulb in the wall sconce browned and flashed, nearly burning out. On the desk, a transistor radio squealed and crackled without being touched. For a brief moment, the whole room came alive with the electric surge of angelic hurt.

Dean looked around the room with wide eyes, putting up his hands in surrender.

"Yeah, alright, Cas," Dean placated, "you're right. It's not funny. Now calm down, before we both go nuclear."

Castiel stared at him and breathed deeply. Gradually, the buzzing died down and the electronics went quiet. When the angel spoke, it was with grave purpose.

"I don't appreciate your blasé attitude toward this . . . situation."

Dean held his arm and nodded.

"I can see that."

"I mean it, Dean."

"I know you do. Look," the hunter stood, still clasping the mark on his arm, "I get it. I'm off the reservation. This thing has got me on a hair trigger and I don't know when I'm gonna go off. But what I do know is this: Cain turned me into a loose nuke, and he meant for me to blow tonight. But I didn't. I kept it together, and I've still got some marbles left, can still count backwards from ten, whatever. And I know that's small comfort given what the mark has gotten me to do, but dammit if I'm not going to take it as a win."

Dean's voice was breathy and shaking. Trying to steady himself, he turned to brace his hands against the desktop.

"Cas," he went on, "if I don't get to have a laugh and a smile despite this mess, I'm gonna lose my freaking mind. But don't you ever mistake that for me not taking this shit seriously."

Castiel sat in brief silence, then apologized.

Dean rubbed his eyes and shook his head.

"It's not your fault, Cas, I knew it all might go to hell like this."

The smile that broke across the young man's face pulled at something deep in Castiel's being. He swallowed heavily and looked at his knitted hands.

"Dean," his said, but the hunter was busy pouring himself two fingers of whiskey.

"Dean."

The young man turned, "What, you want some?"

Castiel just looked at him.

"I'm going to find a cure, Dean."

A soft look passed across the hunter's face but was gone before the angel could place it. If he had to guess, he'd bet it was pity. Then again, human expressions were still a bit foreign to him, despite all his time living among them.

Dean offered no help, only tilted his glass at him in a mock-toast before downing its contents in one go.

"To a cure," he said, setting the glass down on the desk, though he didn't sound as though he believed there was one.

Castiel nodded mechanically, echoing, "To a cure."

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~dances-with-cacti