"Come on, Sammy!" Dean's voice rang out down the long, tiled halls. "Let's have a beer, talk about it… I'm tired of playing. Let's finish this game!"

Sam struggled to steady his breath, eyes flicking down the hall uneasily. But it was empty—where? Whether due to a hunter's instinct, luck, or because he'd heard the faint, uncontrollable, readying intake of breath behind him, he whipped around, ducking barely in time to avoid the heavy swing of a hammer. It collided with the brick in a loud clink. In the same heartbeat, reflex snapped Sam's knife upward—against Dean's throat—but he caught himself before it could delve further. He stared at the blade for only a blink, adrenaline pumping madly through his veins and narrowing his vision, before his eyes slid up to his brother's. A thread of shock weaved through Dean's face, melded with irritation at his failure—at the foil of his perfect swing. Then, with the ease and speed of donning a mask, a taunting smile curled his face.

"Well… look at you." Dean watched, waited. Amused. Calculating. Curious. Wary. Entertained. "Do it." His tone was cloaked in indifference, but beneath it, Sam caught a wisp of… sincerity. Desperation. "It's all you."

They both knew the outcome before Sam's knife so much as twitched.

No matter what Dean had done—no matter what he'd become—Sam would never… he could never kill his brother. Even if he knew it was what Dean would've wanted, before he'd become this thing. Even if, were their roles reversed, Sam knew he'd want the same thing.

His hand trembled. His lip curled with the bitter decision. He stared at the knife, then at his brother. He knew what it likely meant.

But he couldn't do it.

Sam lowered the blade, and Dean's eyes flicked black as a cruel smile claimed his face.

In a blur of motion, Dean ripped the knife from Sam's hands and rammed his brother to the ground, his head snapping violently against the tile. Instinctually, Sam tried to shove himself away, but the world spun, and Dean was atop him in a mere heartbeat. He pinned Sam with a foot on his neck and a knee on his chest, then as his little brother choked for breath beneath him, Dean admired the demon-killing blade, twirling it to catch the light. With a glance downward and a wink, Dean slowly drew it across his own wrist.

If Sam's vision wasn't a rapidly fading blur of light, and his thoughts weren't abuzz with lizard-like panic, he might have wondered at what Dean was doing.

Casually, unhurriedly, Dean lowered himself into a crouch, only slightly easing the pressure on Sam's neck. "How does this go?" Dean grinned at his brother's purpling face, "You were gonna give me some more of that magic blood, and then you were gonna do something a little like this, right?"

Dean shifted his weight and at the instant Sam gasped for air, Dean covered his brother's nose and mouth with his bloodied hand and wrist.

As Sam's lungs fought for oxygen, his mind scrambled for an explanation—but the second the old, familiar stench of sulfur filled his senses, it clicked. He grabbed blindly at Dean's arm, trying to fold his grip with a strike to his elbow, but his vision was shot, and his limbs couldn't seem to coordinate quite right. The coppery tang coated his tongue. He tried to plant his legs so he might flip Dean, but it felt like it took eons to position his body properly. Before he could buck Dean off and buy his brain even a single gasp of oxygen, he felt the thick, coppery liquid slide down his throat. Tears of panic wet his face, and in the back of his mind, he found himself praying that Dean was human enough that it wouldn't work.

Then, a familiar shudder in his veins—a cold flash of recognition along every cell. He felt it stir, and he wanted to scream. To weep. To laugh. To curl into a corner and give up. To escape his skin and flee. To close his eyes and listen to it hum inside his veins. The old, long-suppressed thrill. The power.

Dean's grip vanished almost instantly, and the older Winchester straightened, laughing, "Feels good, doesn't it? I know how much you missed it."

In the absence of Dean's constraining grip, Sam's lungs heaved to compensate for the stolen air, his brain still dizzy. He didn't move, not at first, not even to open his eyes as his breathing gradually steadied. His mind refused to depart from a shrieking protest: no. No, no, no, no. It couldn't be real—it couldn't be, it couldn't be. His heart hammered in his ears—he tried not to hear it, not to hear the blood, not to smell it, not to crave more.

"Take your time—I know it's been a while." Dean bent beside him, "What, six years now?" His smirk was loud in his voice, "Or maybe only five. Didn't your old pal Lucifer sneak you some in the Cage?" Dean cocked his head, the taunting delight lacing each word, "Ohh, right, that was only when you asked him really nicely."

The horrible chill that clawed across his flesh and crushing nausea that clutched at his gut finally assembled his desperate thoughts into an action. He rolled to his side, pushing two fingers down his throat to try to expel the blood, but a part of him mocked that it was already too late. The burning chill already raced through his veins, stretching to the tips of his fingers, igniting every atom in an exhilarating blaze.

Apparently unwilling to risk Sam's successful purge, Dean reached for his shoulder, ready to yank his arm from his throat, "Now, now, let's not—"

As soon as his hand clasped Sam's skin, the latter flung out his own arm, and Dean flew backwards, slamming hard into the wall behind him. He grunted at the impact that fractured the tiles behind him, then laughed.

Sam's arm was still suspended, and he stared at it shakily, at the reflex he hadn't intended.

Dean rolled his shoulders and cracked his neck, then started back toward Sam. Before he could garner even a few steps, however, Sam flexed his fingers, his face twisting with the effort as he again flung Dean against the wall.

Dean struggled to raise his head, managing only a few inches. He grinned like a cat, eyes fixated on his brother, "Like riding a bike, huh?"

"Shut up," Sam ground out, trying not to let himself relish the strength coursing through his blood. It's not strength, he countered silently, it's weakness. It's poison. It's evil. He needed… he needed a plan.

"You didn't think I was just going to kill you, did ya?" Dean shook his head, "Nah, that'd be too easy. But, luckily for you, I had plenty of time to think about exactly what I wanted to do with you. Not like you gave me a magazine to pass the time between your little treatments. As a matter of fact, they're what inspired me."

Sam felt a trail of blood leak from his nose as his head pounded violently. Thinking became only exponentially more difficult, like trudging through an ocean of solidifying concrete. He knew it was from more than just what was probably a concussion—he couldn't hold this forever. He couldn't hold this for a few more minutes.

"I noticed you weren't using your own blood…" Dean remarked, twirling his wrists—perhaps against the ache of the restraint, or to test the strength of the constriction. "You used yours for Crowley, but then, at that time, you were brimming with Trial juice. And, of course, worst comes to worst—it was Crowley." Dean's eyes skated over Sam, evaluating, mocking, "But you're not glowing with Trial juice anymore. Now you're just back to regular old, demon-blooded Sam. And how can you cure a demon when your blood's no better than theirs?"

Sam gritted his teeth. It was true—he hadn't known if his blood would work, and he couldn't risk it. He didn't know if the Trials had cleansed him of the wretched infection—he couldn't be sure, not until today, anyway. But, deep down… he'd still felt it. Though he'd tried to dismiss it as a phantom of his mind, the dark still lingered.

He needed a plan. But he couldn't depart his will for more than a blink—he couldn't move but for the waver of his arm.

"Do you think, if you donated blood, you could kill someone?" Dean mused, "I dunno that 'demon' would come up on any of their standard blood screenings." Dean cocked his head, "Don't you wonder what'd happen? Would they, I dunno, burn up from the inside? Or just get sick and die? How long would it take, y'think?"

"Shut up," Sam repeated, his voice tight beneath the strain. Dean still tugged against his hold, though he couldn't find any purchase—yet.

"I mean, surely you've thought about this before," Dean continued, scowling at another failed yank against the invisible restraint. Then, surprisingly, he eased his struggle and turned his focus entirely onto his brother. "This," his eyes flicked black, "This might be all new to me. And it's… eye-opening, really." With a blink, they returned to a cold green, "But for you? You've been this," he jerked his chin upward slightly to gesture toward Sam, "For forever."

Despite Dean's sudden lack of resistance, Sam couldn't afford to slacken his grip. He glared at his brother, trying to ignore his taunts. "You're just sick, Dean. But we're gonna get you better." He just needed to hold him a little longer…

Dean grinned, "You can't lie to me, Sam. I know you're enjoying this—the blood. I can see it on your face."

"You don't know what you're talking about," Sam refuted, managing to push himself to his feet, his arm still extended.

Dean's smile only grew, "See, the difference between you and me is you… you don't need a Mark. The evil's inside you—it's a part of you. It's just who you are." Dean shrugged, as though to deflect any blame or hurt onto the truth of the statement, even as Sam twisted his head away. "And all a little black-eyed blood does is help wake it right on up. Or maybe it just gives you an excuse."

"Shut. Up." Sam curled his fingers to tighten the constriction—Dean grimaced, but he recomposed into cool arrogance in a matter of seconds.

"I mean, just look at what you did to poor old Lester. And you weren't even hopped up on demon blood then. It was all you." Dean dragged the words, then tilted his head, "How many more 'Lesters' are out there, Sammy?"

Sam clenched his jaw. He couldn't play Dean's game. He had to focus. Just a little longer.

"You're so busy trying to fix me, you can't even see you're far more screwed up than I am."

It's just a demon. He reassured himself silently, it's not Dean. But hearing the words in his brother's voice gouged deeper than he wanted to admit. Just a little longer. He just had to hold him a little longer.

With a cruel grin, Dean sneered, "Which one of us is really the monster?"

Before he could restrain the impulse, Sam's arm snapped back and Dean hurtled across the room, crashing against the ground yards away, his limbs tangled as his momentum carried him several more tumbling feet…

…right into the path of a familiar angel, who lurched back to avoid collision, head twisting instantly toward whatever had tossed Dean so violently—his eyes narrow, then wide.

"Cas," Sam breathed, though shame and trepidation quickly tempered his swath of relief.

Despite his stark confusion and visibly escalating concern, Castiel tore his attention away from the younger Winchester to hastily evaluate the demon on the ground, who grunted in pain as he tried to find his footing. Not granting him the chance, Castiel snatched Dean's arms even as the latter planted them to stand, yanking them behind the dazed hunter's back to latch a pair of etched handcuffs on his wrists.

Dean snarled at the click, but he couldn't escape the angel's grip, couldn't coordinate the strength to overpower Castiel's quick subdual. Yet, his roar of frustration quickly morphed into a cackle. He grinned at Sam across the hall, taunting, "Hit a sore spot, huh?"

Sam didn't reply, and he didn't answer Castiel's questioning gaze. It was difficult to raise his eyes from the floor at all, difficult to keep from checking his forearms as though he might see the infection worming beneath his skin.

"Well, I guess someone finally decided to join us." Dean turned his attention to Castiel, his lips still curling in smug satisfaction. "Did you decide we're worth your time now?" Castiel's jaw twitched, but he said nothing, merely casting another glance toward Sam. Dean pointedly took note of the handcuffs, then gazed up at the angel, "I gotta say, Cas—I didn't peg you for the kinky type, but hey," he raised his shoulders with an acquiescing smile, "I don't judge."

Cas rolled his eyes, grabbing Dean by the shoulder and tugging him to his feet, "Get up."

"I mean, I'm down for anything once," Dean chuckled as Castiel forced him to stumble down the hall. The angel hauled him through the storage room, marching him back to the hidden dungeon and right to the chair at the center of the devil's trap. Sam followed several feet behind, ready to yank Dean to the ground if he somehow slipped Castiel's grasp, while disgusted with his willingness to use the curse all the same. But he couldn't afford to lose Dean again—not now.

"I know you're not really familiar with the whole classy thing," Dean started, his expression cruel, as Castiel exchanged his handcuffs for the heavy manacles bolted into the concrete. "But normally, you take a guy out to dinner before you lock him up in a sex dungeon."

Castiel tested the security of the shackles with a harsh tug, then met Dean's gaze, "Shut up."

Without waiting for the reply, Castiel turned back toward the edge of the room, where Sam lingered in the doorway. The angel frowned at Sam, his voice low, "What happened?"

"Sammy got a little hungry," Dean inserted, his sneer drenching his tone. "Couldn't help himself to a little demon blood, could he?"

Sam bit his lip, murmuring low in explanation to Castiel, "It wasn't like that."

The angel stared at him for a long moment, his gaze dropping a slight degree, before flicking back up to the hunter's eyes. Self-conscious, Sam wiped a hand over his mouth, shame crawling along his spine at the cling of dried blood lingering like a scarlet letter.

"Did you drink demon blood?" Castiel asked, both tone and expression guarded, his body tense and wary.

Sam gritted his teeth, shifting his weight uneasily as he insisted louder, "Yes, but… it wasn't like that." Clearly he knew the answer, so why did he bother asking?

Castiel scrutinized him a few more seconds before nodding once, "Okay, Sam."

"It wasn't like what?" Dean interjected again, apparently unsatisfied with the response, "You mean, you didn't want it? That you didn't enjoy it? That you don't want more right now?"

Sam's hand bunched into a fist, his heart thrumming. He could feel the power like a snake winding along his veins and he—no. He breathed a slow exhale, but it didn't help—not enough. Feeling Castiel's gaze on his back, he stalked to the table in the corner of the room, flipping open the cloth case to remove another syringe, already readied with purified blood. As he turned, he squeezed the air from the tube until blood dripped from the needle—he forced his focus away and started toward his brother.

He could fix this. It would work, Dean would be back, and they'd… they'd figure the rest out. It would work. He raised the syringe, exposing Dean's neck by forcing Dean's head against his shoulder—not harshly, but not gently either.

"Don't," Dean met his gaze, and this time, his face, his tone wasn't disparaging or cruel, it wasn't mocking or indifferent. It was fearful; it was somber. Dean was scared. Terrified of the cure succeeding, of what it would mean. "Please." It somehow drove deeper than the insults.

Sam paused only a heartbeat before he plunged the needle into Dean's neck and emptied the syringe into Dean's veins. He closed his eyes as he turned, trying not to hear his brother twist and grunt and cry out in agony.

"Sam…" Castiel started softly, but the Winchester shook his head, catching the angel's gaze for only a moment—long enough, apparently—to shut down the inquiry. Sam knew Cas must have a dozen questions—fair questions, questions that deserved answers. But right now… he couldn't.

Sam leaned against the table, folding his arms and staring at the floor. This time, he couldn't leave the room. He couldn't risk it. So he waited in silence as his brother screamed and writhed in torture, as he begged and cursed Sam's name when his sounds were coherent enough to shape words, and he waited, and he waited, until the screaming stopped.