Title: Final Straw
Author: Zubeneschamali
Rating: T (language, violence)
Summary: As hard as he tried, Dean couldn't erase the fact that it was his little brother he was preparing to shoot. Evil!Sam, captive!Dean, and the end of the world as we know it.
Spoilers: Through 4.14, "Sex and Violence".

A/N: Never thought I'd write an evil!Sam story, but a single line of dialogue popped into my head, and 30,000 words later, here we are. The story title and lyrics with all their foreshadowy goodness come from the song of the same name by R.E.M. I owe ster1 big time for her freakin' awesome beta reading and for asking me lots of hard questions that led to a better story. Thanks also to Kasman for being the guinea pig and helping with the details. You both rock.

Disclaimer: I do not own the Winchesters or Castiel; they're the property of Eric Kripke and the CW folks. Nor do I own Lilith or Lucifer, but I'm pretty sure Kripke doesn't, either. At least I hope not.

Bonus disclaimer: I know there's a lot of fics about The End out there, and I can point to "What If" by SavingFaith and "War Zone" by darksupernatural as two (great) stories that definitely inspired me. I have not yet read SavingFaith's "Losing My Religion", so any similarities between my story and hers are a really big coincidence. No infringement is intended of either story or any others on a similar theme. Also, note the lack of a deathfic disclaimer.

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as I raise my head to broadcast my objection
as your latest triumph draws the final straw
who died and lifted you up to perfection?
and what silenced me is written into law.

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The worn chain link fence still sagged in the same places it had three years ago. Dean briefly wondered as he climbed it if the local kids had stopped daring each other to come here once the ghost of Dr. Ellicott was gone. More likely they had been careful to leave things as they had found them. People had a hard time resisting the lure of the forbidden, even when they damn well knew better.

His leather jacket caught slightly on the rusted metal of the fence, and he paused to loosen the fabric. There was no sound from inside the old asylum, and the street behind him was as silent as the grave. People were keeping inside after dark these days, huddling around their televisions and computers and trying to figure out what the hell was going on.

Hell was actually a pretty good word for it.

Dropping to the ground as silently as he could, Dean felt horribly exposed. There weren't any faces at the windows, black-eyed or otherwise, but he had no doubt the building was inhabited. The clues left in his Iowa motel room were too obvious to ignore. They were also too obvious for this to be anything other than a trap, given what had happened here three years ago, but he had no choice. If what he'd been hunting for the past week and a half really was here, he had to act now.

It hurt like a knife in his chest to think of this as hunting, but the words If I didn't know you... sprung into his brain before he could help himself. Dean swallowed hard and gripped the handle of his weapon more firmly. It should have brought him relief or even joy to be holding Samuel Colt's special gun once again. After all, he had brought down the yellow-eyed demon with it, ending a lifelong quest of at least three Winchesters. On the other hand, an ally had paid a steep price to return this gun to his hands, and even though it was someone he had never expected to mourn for, it was still a blow.

And then there was the matter of what he was planning to do with the gun.

Dean grimaced and moved forward, hardening his heart and his mind. Based on the events of the last couple of weeks, ever since it became clear his brother's disappearance was connected to something darker than Dean could have ever imagined for him, he'd had to face the bitter truth. John Winchester's warning had been justified, the promise he'd drawn from Dean prophetic. Either Sam was possessed, or he had slid right down that slippery slope into being what his father had most feared. Either way, it meant Dean had failed to save him, and now far more people than him were paying the price.

But saving Sammy hadn't been the entire promise.

He slowly pushed open the front door, unsurprised to find that it gave easily. The floor was thick with dust, but there were a number of different footprints crossing the entryway. There was also a wider swathe of cleared floor, as if something had been dragged through the space. Some of the prints went down the side hallway to the south wing, some towards the staircase leading to the upper floors, while the north hall looked untouched.

He turned to his right. The south hallway was in worse shape than last time he'd seen it, if that was even possible. The walls were a mixture of peeling paint and mildew, piles of unidentifiable debris stacked at their base. He remembered holding the EMF meter out in front of him, Sam walking beside him with the camcorder, both devices spitting out evidence that they were not alone. There'd been a constant feeling of someone watching them, and the camera had confirmed the existence of dozens of spirits. Now, the place felt empty—at least of ghosts.

Coming to a junction in the hallway, Dean slowed to a stop and listened. A steady drip of water from behind one of the walls was all he heard. He tried to remember the layout of this place, but it had been so long ago—forty-three years for him. Damn, sometimes he was impressed he remembered anything pre-Hell, given how long ago it had been.

Not that he was likely to forget the image of his brother plugging him with a chestful of rock salt and then standing over him and pulling the trigger of Dean's own gun. No, those memories had stayed with him, carefully preserved like a damn scrapbook page. He briefly wondered if the rage and hatred he'd seen on his brother's face way back then had been an early warning sign that he should have paid more attention to.

Like hell it was, he snapped at himself. No, Sam had disappeared like this before, had been turned into something he wasn't by that black-eyed bitch who'd taken such delight in turning his brother against him. It happened before.

He kept telling himself that, like he had ever since his little brother had vanished from their motel room in the dead of night. Like he had after Uriel had suddenly appeared in the Impala's passenger seat a few days later, talking about the war and seals and Castiel off on a mission. Not that Dean had given a crap about what the angel was saying until he mentioned Sam. Then he started to pay attention.

And he didn't like what he heard.

Uriel had explained to him with less condescension than normal that they were down to eight seals because a tall, brown-haired man fitting Sam's description had been spotted earlier that night casting the spell that broke the ninth. Dean had refused to believe him, but a secondhand vision from the angel had shown him his brother's features on a man opening a goddamn crack in the ground. That night the news had been filled with reports of the 7.6 earthquake that had rocked Northern California, shattering buildings and water mains and freeway overpasses and looking like it was going to be equal to the 1989 quake in terms of casualties.

The epicenter was on the campus of Stanford University.

The days after that had become a dark blur of almost no food and even less sleep. It took a two-fingered forehead touch from Uriel to put him out, but even that only lasted a few hours. Dean spent his time driving blindly from one state to another, for once in his life following the news—because the events Sam had gotten caught up in (he stubbornly refused to believe Sam had caused them, no matter what the dark-skinned angel said) were big enough to be noticed by more than hunters. The newscasters were more confused than alarmed at the strange weather and odd animal behavior, but Dean had the feeling it was only a matter of time before the public at large became aware that something big was going down.

Especially once the last of the seals was broken.

Dean shook off the thought and steadied his hold on his weapon before cautiously peering around the corner. The hallway was clear in both directions, and he still heard nothing but his own too-fast breathing and the steady drip from the long-leaking pipe. He couldn't remember where this hall led, but he supposed it didn't matter. After doing a mental eeny meeny miney moe, he shifted his weight to move to the left.

The scrape of a footstep on the concrete directly behind made him freeze for a second before whirling around sharply, bringing the Colt to bear on—

Sam, who stood not ten feet in front of him.

He was wearing the same scruffy jeans and layers of t-shirt and flannel that Dean had seen him in all his life. But his bearing was different: shoulders back, head held high, arms loosely down at his sides, and fingers slowly flexing as if he was itching to wrap them around somebody's throat.

And his eyes were amber yellow.

Dean felt his heart drop somewhere below his stomach as he wrapped his fingers more firmly around the gun.

"Hey, Dean," Sam said casually, blinking. Now his eyes were their usual warm blue-green, leaving Dean to wonder if it had been a trick of the light.

"What's goin' on here, Sam?" Dean demanded. The words came out roughly, and he cleared his throat as he settled into a familiar stance: weight on his left foot, braced with his right leg towards the back, arms held out in front of him, aiming at his target.

"Been waiting for you," came the easy reply, followed by a scoffing noise. "Took you long enough. I even picked a place with some fond memories so you'd be able to find it again. Betcha got lost anyway."

The younger man didn't seem alarmed to have a gun pointed at him, and from the flare of recognition in his eyes, he obviously knew it was the Colt. That chilled Dean right down to the bone. How could whatever it was in Sam not be freaking out at having this weapon pointed at him, knowing what it could do?

For the first time, Dean wondered if he had made a mistake in coming.

"So what else have you been picking out of Sam's brain, huh?" he asked. "Besides the hottest libraries in town?"

"Oh, you think this isn't me?" Sam's eyebrows went up as he gestured down at himself. "You came here to play hero and save me from another siren or something? Dude, get a clue." He hooked the fingers of his left hand into his shirt collar and pulled it down over his collarbone. The swirling tattoo was intact on his chest. "Nothing's getting in here that I don't want to." He let go of the cloth and jerked his chin towards Dean. "Gimme the flask."

Dean hesitated for a moment, then figured as long as he had the gun in his hand, he still had the upper hand. Continuing to hold the Colt steady, he pulled his silver flask of holy water out of his inside jacket pocket. "Christo," he said as he tossed it.

Sam snatched the flask out of the air without hesitation. "Cross shapeshifter off the list. Oh, and demon, too." He opened the flask and poured a little water into a cupped hand. As if it were aftershave, he splashed it on his jaw and cheeks.

Nothing happened.

With a wink, Sam took a swig from the flask and smacked his lips. "Ah. Refreshing."

Dean swallowed, his mouth dry. He had been so sure it wasn't Sam. Even after everything Uriel had said and shown him, Dean had been sure there was another explanation. But now...

"I can see the gears turning in that tiny little brain of yours, bro. You're wondering what's going on, what's possessing me." Sam capped the flask and tucked it away in his front pocket. "And the answer is: nothing." He spread his arms wide. "This is one hundred percent. Pure. Sam."

Dean's lip curled up in response to the words that he'd never known his brother had heard in the Wyoming cemetery. "Then I better hear a damn good explanation from you about what the hell is going on out there. Bro."

"I haven't really gotten out much lately," Sam replied with a light shrug. "People to meet, worlds to conquer, that sort of thing. Why don't you fill me in?"

"Like you don't know," Dean retorted, taking a step forward. "You're the one who's been out there breaking the damn seals. Tell me you have a good reason for that."

Sam moistened his lips. "I do," he said simply.

"You wanna share?" Dean growled to cover the stomach-sinking fear those words gave him as he raised the gun slightly higher and prayed that he would have the strength to do what might need to be done here.

"Not particularly, no. At least not right now." Sam slowly crossed his arms over his chest, and Dean was sharply reminded of just how large his brother was. As muscular as his frame had gotten over the past couple of years, it seemed to have grown even more in the past two weeks.

"Then tell me what the hell I'm supposed to think, huh?" His voice was rising, and Dean forced himself to keep it in check. "The Book of Revelation is coming to life outside, and you seem to be there every time something happens. California's had the Big One, half of New Mexico is on fire...damn it, the whole state of Kansas is being eaten up by locusts."

"Huh." Sam cocked his head slightly to the side. "I thought you hated Kansas."

Dean stared at him in bewilderment. "That is so not the point."

Sam lightly shrugged. "Actions have unintended consequences, Dean. Like leaving a trail so that you could find me. You being here is the expected result. What you came bearing with you—that was unexpected." He nodded at the Colt. "Thanks, by the way. I really appreciate it."

"What are you talking about?" Dean snarled back, gripping the gun tight enough that his hands ached.

"I wasn't sure how I was going to get a hold of it," Sam replied easily. "You've made things a lot easier for me."

A chill ran down his spine. Uriel hadn't tracked down the Colt and fought off a host of demons for Dean to hand it right over. The last thing the angel had said was a prayer that Dean would have the balls to use it when the time came. Dean hadn't known that angels could use that kind of language, but then Uriel had collapsed and there was no way to ask him about it.

Even though Castiel had said it was possible, he'd never thought he'd see an angel die in front of him.

The memory brought a wave of despair with it, and Dean clenched his jaw so tight that it hurt. "Guess Uriel was right about you," he spat out.

For a moment, Sam looked hurt. "You're still listening to that dick? The guy who called us mud monkeys and wanted to kill a thousand innocent people 'cause he was afraid of me?"

He wasn't touching that one with a ten-foot pole. "I brought this here for you, all right," Dean retorted, his eyes flickering down to the gun and then back up to Sam. "But not like you think."

A mocking smile curved the corners of the taller man's lips. Sam spoke carefully as he said, "The thing is, Dean, if you think you need that, then you should also know that it's not going to do you any good."

Dean swallowed hard. "This gun can kill anything," he said hoarsely. "And you know that."

Sam's eyebrow quirked up. "If you have the balls to use it, that is."

Praying his voice wouldn't break, he replied, "I don't want to hurt you, Sam. I swear to God, I don't. But this has got to stop. You have to stop."

Sam took a slow step forward. "You don't understand, Dean."

"You're damn right I don't!" he shot back. "What you've been doing, who you think you are...We get down to ten seals and then you disappear and up and start breaking them like you're on their side." Moisture crept into his eyes and he furiously blinked it away before slipping his finger off the trigger guard and onto the trigger. "All I know is that you're not Sam anymore. My brother is gone."

He'd said that before under the poisoned spell of an ancient being who'd very nearly made him kill his own brother, but the words had still rung with an echo of the truth. Now he was in his own mind and sighting down the barrel, trying as hard as he could to think of this as another target, another thing that had to be hunted.

But as hard as he tried, Dean couldn't erase the fact that it was Sam's face he saw in front of him. It was his little brother that he was preparing to shoot.

"Dad made me promise." Dean spit out the words, trying to convince himself as much or more than anyone else. "You made me promise." Then he spoke the words he never thought he would have to say. "And I'm here to carry out my end."

"You think you can do that?" Sam asked with a raised eyebrow, taking another step towards him.

"Stop right there," Dean demanded. "Don't come any closer."

"Or what?" Sam asked, his voice growing stronger. "You'll shoot? I don't think you can, Dean."

He lifted his chin, eyes flashing, drawing on the memory of all that had happened over the last two weeks to strengthen his resolve. "Wanna bet?"

And his finger tightened on the trigger.

A second later, Sam's hand shot out and to the side. His eyes never left Dean's as the gun flew out of his hand to clatter harmlessly against the floor. "I can't let you do that," he said calmly.

Dean stared after the gun for a moment and then back at his brother, his stomach sinking, his hands now without a weapon. "Where did you learn to do that?" he asked, trying for casual as he slowly snaked his right arm around behind him for his own pearl-handled Colt, figuring silver bullets from a standard gun were better than nothing.

But this time his voice did crack, and the fear of his brother he had sworn he would never have came leaking out through the gap.

Sam must have heard it, for he gave a knowing smirk as he advanced more confidently, stopping within arms' reach of him. Dean took an involuntary step back, stopping with a jolt as his back hit the wall of the hallway, fingers closing around the grip of his weapon.

There was nowhere to go.

Behind Sam, two men entered the hallway from a room a few yards back, eyes coal-black and menacing. Sam started to turn his head towards them, paused as if listening to something, then focused back on Dean. "Sorry, Dean," he said. Then his eyes narrowed. "But you're not standing in my way anymore."

And he raised his hands, fingers spread wide, and pushed.

Dean had been held up against walls by supernatural forces plenty of times, but it had never hurt so much. This time he had the added bonus of the anguish at how it was being done to him: how his own brother, whom he had raised and loved and trusted and sacrificed his life and his soul for was now standing on the side of the demons who were watching with undisguised glee.

His vision started to narrow, dark spots dancing in front of his eyes as he watched Sam's hands slowly curl into fists in time with the ebbing away of his consciousness. He feebly tried to lift an arm away from the wall, unsure if he was reaching out to his brother in anger or in supplication, but it was useless. His strength was draining away as fast as his awareness.

The last thing Dean registered before darkness descended over him was the utter blankness in his little brother's eyes.

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*big gulp* I think I'm ready...go ahead and click on that review link...