Warnings: non-con, animal traits (knotting), post 6x22, kidnapping, bondage and torture, potential future mpreg

***
Sam woke to the sudden whoosh of displaced air. He blinked and didn't move, eyes slowly tracking over his surroundings. He was sprawled out in a cell, one arm stretched out in front of him and blocking his view. What he could see sent his heart pumping: cold stone floor, no window, no door. There were delicate light fixtures on the walls, glowing with a warm, golden light, incongruous with the rest of the room. The sound of a sharp inhale seemed to echo off the walls, and Sam pushed himself upright, searching for its source.

Castiel was bent over Dean in the other corner of the cell. The angel- ex-angel- had Dean's face cradled in one hand, slowly rubbing his thumb over Dean's bottom lip.

"Get away from him," Sam said, voice low and angry. The sound of a chain rattling caught his attention as he stood and he frowned at the long line of chain leading from the wall at his back to a collar around his own neck. It wasn't long standing, there was no slack in the chain and he could barely move away from the wall. He rubbed his neck and could barely fit his fingers beneath the heavy band of metal. He settled himself back on the ground in a ready crouch, and the chain fell loose against the wall.

Castiel cast a glance back over his shoulder at Sam, his eyes empty as a scream. He tilted his head slowly, the gesture too-familiar for the monster that had replaced their friend. "Sam," Castiel blinked and turned his attention back toward Dean. "It is fitting that you are awake for this," he said, almost to himself.

Sam caught Dean's eyes over Castiel's shoulder, wide and terrified. Castiel shifted so his hand, pressed low on Dean's stomach, was visible. He pressed down and Dean gasped, back arching off the wall. Dean brought his arms up and swung a punch at Castiel, the motion slow and clumsy. The hit connected but Castiel paid it no attention, eyes flicking between Dean's face and his hand on Dean's stomach.

"What are you doing?" Sam asked, his voice quiet. Something more was going on than he could see. Dean's silence, motions, hell, even his face, so openly terrified spelled out clear as day that whatever Castiel was doing, it wasn't good.

"I am cleansing his blood," Castiel said, serene. He leaned in toward Dean and inhaled, his eyes sliding shut and his face falling into an unfamiliar expression of arousal.

Sam blinked in confusion and then the smell hit him. Bitch, some part of him sighed out, recognition whispering at the edge of his mind. The distinct smell of an unmated Beta filled the air of the cell, Dean's familiar scent changed, overlaid with the powerful scent of raw potential. Disgust roiled through Sam; Castiel was purging Dean of Androgen-D. He was making Dean ready to mate.

"You're sick," Sam whispered, horror stricken. Without the androgen in his system, Dean's body was going to change- had already started changing, from the scent in the air. Sam didn't know how Castiel knew that Dean would develop into a Beta, but his plan was clear. "You can't force a mating!" he yelled, desperate to put a stop to what he knew instinctively was about to become his brother's rape.

"He'll love me." Castiel licked his lips and again scented the air. "He won't be able to help it."

"Fucking- get off, Cas!" Dean was too-quiet, coherent speech an obvious effort. "'m not gonna be some bitch."

Anger shadowed Castiel's features. "You will be my mate," he said with absolute surety. His grip tightened on Dean's face and a white light shone around the hand on Dean's stomach. "Without the suppressant your body will demand it."

Dean's eyes snapped toward Sam, an expression of deep-rooted terror clear on his face. "I won't," he said. "Cas, you don't get it, I-" he cut off with a gasp and arched off the wall, chest heaving. The room stank of ripe Beta.

Sam's cock twitched. Sam blinked and stared down at his lap. He could see the outline of his cock as it swelled and tented his pants. His attention was dragged back to the other side of the cell as Castiel stood tall and shrugged out of his trench coat.

"Castiel- Cas," Sam begged. "Stop this. You know it's wrong."

Castiel ignored him and removed his tie, dropping it carelessly at his feet. His shirt soon joined it, and shirt, shoes and pants followed, until he stood naked in front of Dean. Castiel was hard, cock red and ready between his legs. He stripped Dean with quick, careful hands, totally unconcerned with his nudity, with Sam's pleas or presence at all.

Castiel flipped Dean onto his stomach, the chain connected to the collar at Dean's neck clattering too-loudly in the room. Dean was silent but for his breath, deep gasps that signaled the start of a Beta's heat.

Sam struggled to comprehend what was happening, mind flashing back to an assembly one school had insisted all the kids attend. It hadn't seemed important at the time, a useless lesson on Alphas and Betas in society; Sam was going to be someone important some day, not some moronic knothead or slutty bitch at the mercy of his hormones. He'd been taking Androgen-D since before he knew what it was, a childhood insistence to be just like his big brother meaning he'd been on the hormone-suppressant since he was eight.

Shallow breaths, hormone-stink, raised temperature; Sam couldn't remember all the signs of an oncoming heat, but he knew enough to recognize it when he saw it. He knew enough to know that if Castiel fucked his brother, Dean would be bound to Castiel on a level beyond conscious thought.

The thought of losing his brother- the thought of his brother mind-and-body fucked into loving Castiel- made bile rise in the back of Sam's throat. "He won't be Dean anymore," Sam begged, grasping at straws. "You do this, and what you get won't be Dean. You'll just have some fuck-happy breeder who'll mindlessly follow your every whim."

Castiel settled his hands, sure and easy, on Dean's ass. He spread Dean's asscheeks apart, and the light was strong enough in the room that Sam could see the faint shine of slick. Castiel rubbed the outer rim of Dean's hole, gaze focused on the inflamed rosebud as he spoke. "He will be mine. I will demand his honesty and he will be unable to refuse me." Castiel shifted and Sam's gorge rose in his throat at the sight of Castiel's cock running up the cleft of Dean's ass. Dean arched into the pressure and whimpered, flushed with desperation.

Sam closed his eyes as Castiel leaned in and fucked his cock in, but a tight pressure on his neck had him opening them after a handful of seconds. "You will watch," Castiel said. His voice had lowered with obvious arousal but Sam paid him no attention.

Dean was crying. He was fucking himself back on Castiel, his cock hard and heavy between his legs, but his tears caught the light just as effectively as the slick between his legs. His mouth was slack with pleasure and his tongue flicked out to lick his lips like he was hungry, but that was because of the heat. The tears, the empty look he could see taking root beneath the pleasure- that was all Dean.

"Dean," Sam whispered. He shook himself out of his stupour; his brother was hurting, and Sam wasn't going to let him do it alone. "I'm here, Dean. When this is done, remember that- I'll be here. We'll get through this."

Dean shuddered, at Sam's words or Castiel's thrusts Sam didn't know, and Sam made himself watch. Watch as Castiel grabbed hold of Dean's arms and tipped them backwards so that Dean was perched on Castiel's lap, on full display to Sam's eyes.

He should have felt horrified, and he did. But beneath the horror was a creeping sense of want that Sam didn't understand. Watching Castiel's balls as they slapped up against the flesh of Dean's ass with each upward thrust, the wet sound of Dean's ass as his hole clenched around the cock inside of it, desperate for an Alpha knot. Sam didn't want to see it when it swelled and popped into his brother.

Sam dragged his eyes up and to meet Dean's and let the promise of vengence fill his gaze. Even if Dean got (his mind balked) pregnant, even if Dean was mated to Castiel, Sam wouldn't show mercy. If he caught, Dean wouldn't be able to help, but Sam was more than willing to take up the slack in this case. Some part of him (maybe all of him) just wanted to make castiel pay. The wet trail of tears down Dean's cheeks continued unchecked had Sam choking on rage and his own tears.

Castiel encouraged Dean to fuck himself on his cock and Dean's instincts forced him to obey. Dean was splayed over Castiel's lap, his bare knees pressed hard into the rough ground, red and pockmarked by small stones that his weight had dug into his flesh. Sam could see the dark smudge of bruises on Dean's hips, the faint shadow of Castiel's hands infuriating against the pale of Dean's skin. Dean nipples were dark and tight on his chest, his cock dark against his belly, but his movements were slowing, the desperate, heat-induced edge from a few moments earlier fading into a helpless twist of his hips, as though desperately searching for... something.

Sam's eyes reluctantly trailed down to Dean's hole, red and swollen with heat, and studied Castiel's cock. Castiel was still thrusting, the tireless stamina of an angel meaning every flex of his hips was hard, fast and perfectly timed with Dean's movements. Sam could see the entire length of Castiel's cock every time he withdrew and it struck him, suddenly, that Castiel didn't have a knot. A short bark of laughter broke out from Sam and he met Dean's stricken gaze with his own. "He's not an Alpha," Sam said, relief colouring his voice with black humour. "He's dead-set on mating with you and he doesn't even have a knot to do it with."

Castiel slammed Dean down hard on his cock and Dean's hole fluttered wildly around the base of the cock inside him and couldn't help but notice the slow ooze of juice from Dean's hole leaking unimpeded down Castiel's shaft. There was no knot to stop it, which meant no pheromones that would kick-start a Beta into full estrous. No mating cycle to fuck with Dean's head or heart to confuse his loyalties.

"You're fucked," Sam said with surety. "His body is just," his mind desperately put together pieces of a puzzle he knew too little about, "reacting to the change. This isn't a heat. This is just puberty."

"You're wrong," Castiel growled. His eyes were dark, barely visible over Dean's shoulder. "I triggered this heat, not an Alpha. His body will react accordingly." Castiel's hand splayed out over the pale skin of Dean's abdomen. "There is no other option; he will accept me." His motions were frantic, angry; he didn't fuck Dean like a man sure of the outcome and it slowly dawned on Sam why.

Dean hadn't come yet. He was a Beta being fucked in what Sam could believe was the grips of a genuine, if falsely induced, heat- everything he'd heard whispered about the wild fucking that was inevitable when people stopped taking their suppressants said that Dean should have been a mess, fucked out and covered in his own come as he was bred. But he wasn't. Dean was wet, covered in sweat, tears and the slick from his ass, but there wasn't even a sign of precome on the tip of his cock.

"It's not working," Sam said and Castiel's snarl of rage confirmed it. "Dean's going to come out of this soon. He's going to wake up and he is going to hate you." Sam wanted the words to be true. Was desperate for them to be true. But Dean and Castiel- they had been close, and it took a lot for Dean to burn a bridge, and people hurting him, playing him, wasn't always enough. He'd forgiven Sam, after all.

Sam had more than enough hate for both of them.

Castiel slid his hands under Dean's thighs and lifted him, inhuman strength making the move look easy. Dean grunted in protest as Castiel's cock slid from him in a wet sounding slide. Sam caught a brief glimpse of the inflamed hole winking open and closed before Castiel gently settled Dean onto his back. Dean lifted his hands to Castiel's grip at Castiel's shoulders, the first sign of deliberate movement Sam had seen from him in what felt like far too long. He stared up at Castiel, that same empty look on his face, and Castiel softened under his gaze. Castiel leaned in close, Dean's name a quiet whisper of breath, and Dean spat in his face.

Castiel blinked and the affection bled out of his face, replaced with a cold, hollow desperation. He rolled his hips forward and slid inside Dean again, but his motions had lost any hint of softness he'd had in the previous coupling. He fucked Dean with a brutality that bellied his lack of knot. He tore Dean's hands from his body and pinned them above Dean's head with one hand and slotted his other to Dean's shoulder, where the scar of his mark was just visible.

Dean twitched at the touch but just started to struggle harder, and Castiel growled in frustration. His motions were desperate, but ultimately useless. No knot swelled. No mating-bond was created. Dean's cock had even started to soften, and Sam felt a surge of victory. Betas always wanted their mate- were always receptive to potential mates. Castiel was neither.

That didn't stop him from fucking Dean. Castiel released Dean's hands and gripped Dean's dick in his hand as he fucked him, but Dean just softened further, his body withdrawing from Castiel in the only option available to it. It went on for too long, Castiel's desperation showing through in his obvious, slightly clumsy attempt to target Dean's prostate. Eventually he came, held tight inside Dean's body. Sam might have heard a sob when he did, but when Castiel pulled out his face was calm, collected. His cock gleamed wetly in the light, and Dean's ass was a fucked out mess of juice and slowly leaking come.

Sam strained forward, the pull of his collar against his throat unimportant when held against Dean's stillness, Dean's- hurt. "Let me see him," he said. "Please, Cas, just. I won't do anything, just let me see him."

Castiel stared at Sam, spine straight, and made no move to cover himself. The edge of his foot was touching Dean's calf, and somehow that one point of contact, so careless, brought a wash of tears to Sam's eyes. "Please," Sam begged, pride nothing next to the need to touch Dean, to offer whatever comfort he could.

In less time than it took to blink an eye, Castiel was gone and Sam on the opposite side of the room, his collar bolted into the wall next to Dean's. Dean jerked upright and stared at Sam, his eyes too wide and his skin pale enough to make his freckles stand out in sharp relief. No stubble, Sam realized, and shuddered as the first hint of how this would change their lives after they got out (because they would get out of this) chased around the edges of his thoughts.

"You okay?" Sam asked. He stripped his shirt off and draped it over Dean's shoulders, then couldn't stop his hand from creeping forward to touch the tips of his fingers to Dean's, desperate for contact, for the affirmation that Dean was still here, still alive, still- not broken.

Dean snapped his eyes down to Sam's hand on his own and a full shudder worked through his body. His cock, flaccid against his thigh, twitched and swelled with blood. Sam froze as the smell of Beta-heat rose again in the air, so thick he could hardly breath, let alone think. His own cock was hard- had never softened, he realized. Confusion washed over him and he moved his grip up to Dean's wrist, anchoring himself. "What's happening?" he asked, and his voice was low with building arousal.

Dean's pupils were huge, only a bright ring of green visible around their rim. His voice, when he spoke, was steady, and Sam calmed at the sound of it before his words filtered in. "The Terminator version of you," he licked his lips and Sam couldn't help but follow the motion with his eyes, "He wasn't exactly- responsible. By the time he met up with me he'd stopped taking Androgen at all." Dean laughed and glanced up at Sam from beneath his lashes. "He put even me to shame, practically banged anyone that bothered to stay still for long enough."

Sam's stomach twisted in on itself. "Did he. Am I mated to someone?" Sam whispered, horrified at the thought he'd been mated to some random hookup he couldn't even remember.

Dean shook his head. "Not that I could tell." Relief crashed through Sam. Relief that he didn't have to deal with that and, again, relief that Castiel hadn't been able to do that to Dean.

Sam blinked, and looked down at their joined hands. "That's why Castiel couldn't mate you," he said slowly.

Dean nodded, the motion jerky, stilted. "A Beta won't mate with anyone but an Alpha if the option's available," he agreed. His lips quirked upward, a sad shadow of a smile. "You always do have my back."

Sam gave in to what his instincts were screaming at him to do, and gathered Dean into a hug. He ducked his head down into Dean's neck and ignored the way his cock twitched at the strong smell there. "We'll get through this." They had to.

Dean nuzzled into Sam's neck and the tension bled out of him. "You and me against the world, huh Sammy?" he whispered, and the rough edge of tears cracked briefly through the facade of normalcy Dean was always so desperate to maintain.

Sam squeezed his brother close. His cock was still hard. So was Dean's.