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A flash of light. A throbbing, brimful feeling. A spreading, yawning depth that reaches beyond Castiel's understanding.

Lucifer's grace is magnificent.

It's corrupt -- bone-yellow instead of blue-white, threaded with malice and deceit, hardened by resentments that stretch back to the dawn of creation. But it pulses with strength and vitality and intent, glitters with the sheer celestial perfection it once possessed. Michael might have been God's strongest, his most dutiful, but Lucifer had been his favorite. Lucifer had been created to reflect all of heaven's glory and radiance and might.

Castiel is terrified.

You should be, Lucifer says, as he fills Castiel completely, as his grace hums and throbs inside Castiel's body. I can defeat the Darkness. And I will. But what comes after -- well. Humanity's in for one hell of a surprise.

In the pit of his own body, the bare sliver of space Lucifer has allowed him, Castiel shivers.

Get it? Hell. One hell of a surprise. The cage gutters around them like a candle, then winks out with a whiff of sulfur and myrrh. Lucifer twists Castiel's mouth into a smile. Come on. Don't get shy now. It's okay to laugh.

The brand on Castiel's chest aches, but the pain is distant and muted. His body is no longer his.

You should've known this was a mistake. I mean, screwing up does seem to be your favorite trick, but this -- you weren't thinking. You were desperate to get the Winchesters away from me. Desperate to do something about the Darkness. It's pathetic, really -- how badly you want to be useful.




"You all right?" Dean asks.

Lucifer hesitates for moment, his grace piquing with curiosity at the longing curled around Dean like a snake. "I think so." Castiel gouges at him, riotous with anger, but Lucifer just bats him away. He lets a smile tug at the corner of Castiel's mouth. "I will be."

Dean gestures at the Impala. "Can I give you a lift?"

"You two go on ahead. I'll catch up."

Dean nods. Longing floods out of him in a furious rush, ebbing away like the tide as he turns toward the car. "Okay."




Lucifer traces Castiel's fingers down the line of Rowena's throat. She smells like lilac and candle smoke. Castiel tries to wrench away, but Lucifer is implacable. Inexorable.




Dean sighs, rubbing his forehead as he looks up from his notes. It's a handwritten translation of one of the ancient texts Cas found in Gaza. He catches Cas' eye before grabbing his empty coffee mug and heading into the kitchen. Longing shimmers around him like mirage-heat on the horizon.

He loves you, Lucifer observes. He says love like it's a novelty, like it's a deficiency, like he never loved so deeply and fiercely that the force of it ripped heaven in half. Like it didn't almost destroy the world. That's interesting. A match made in hell.

Lucifer burns like a forest fire, consumes everything around him like a collapsing star. So far, it's been all Castiel can do to simply weather the maelstrom; now he marshals his waning strength, scratching and clawing at Lucifer's grace with everything he has left.

Relax. I'm not going to hurt him. Not yet, anyway. Lucifer's grace buzzes, an approximation of a laugh. The Darkness seems... fond of him, and that'll help me find her. After that -- well. It depends on how useful he is. How obedient.

Castiel surges up, fearful and seething, but Lucifer shrugs him off with ease, a movement so minute his essence barely ripples. He seems to sigh. Dean shuffles back into the library with two steaming mugs of coffee. His fingers brush Castiel's as he hands one over, and a bolt of want arcs through Castiel's body like lightning screaming across the sky. It's a carnal, visceral reaction, and it makes Lucifer smirk.

Tell me, Castiel... Have you two ever --" Lucifer pauses, his grace humming with innuendo, hinting at a crude gesture "-- done the horizontal tango? Made the beast with two backs?

They have, but only twice -- shortly after Cas returned from purgatory, and again when Cas was human, when Dean visited him in Idaho. Both times, Castiel had been astounded by how tender Dean had been, how passionate, at the things Dean had whispered against his skin, at the myriad of sensations Dean had wrung from his body. He'd been equally surprised by how quickly Dean had folded in on himself afterward, how determined he'd been to pretend like nothing happened.

Castiel's memories flood out unbidden -- the spray of freckles across Dean's nose, the honey-hue of Dean's hair in the sunlight, the way Dean's mouth had felt sucking bruises on the inside of his thigh, the noise Dean had made as Castiel inched inside him, the warmth of Dean's soul against the curve of his wing.

Lucifer laughs and laughs and laughs.




"You sure you're okay?" Dean asks.

Castiel's mouth twitches. Then Lucifer says, "I'm fine, Dean." His voice slides over Dean's name like a caress, so intimate it makes the shreds of Castiel's grace cringe and writhe. "Why do you keep asking?"

"'Cause you ain't been yourself since -- you know. Since we got back from hell. You just seem... I don't know. Different."

"I'm fine." Inwardly, Lucifer bristles -- it galls him, being questioned by a human -- but he works a concerned, earnest expression onto Castiel's face and continues, "Now, tell me what Amara said to you."

"C'mon, Cas. I don't --"


Dean sighs and rubs the back of his neck. "She, uh -- she said we were bound. She said she couldn't be resisted."

Lucifer almost snorts; his grace quivers as the noise dies in Castiel's throat. "Interesting. Tell me, when you're around her... how do you feel?"

Dean rubs the back of his neck again. A darkly smug sensation suffuses Castiel's body, and Castiel suddenly understands. Lucifer doesn't care what Amara said. He just wants to feel Castiel's discomfort. He just wants to see Dean squirm.

"Nothing," Dean says finally. A faint flush is burning along the line of his jaw. "I mean, when she's around, I'm -- I don't feel much of anything. I just -- everything gets kinda quiet."

"You're not scared of her?"

"Right now? Yeah. I'm scared shitless of her. But when she's in front of me, I just -- like I said, everything gets kinda quiet. Cold." Dean clears his throat. "I just feel kinda --" he gestures at his chest "-- empty, I guess."

"She can't be resisted," Lucifer murmurs under his breath. His grace stirs thoughtfully. Then he tips Castiel's head to the side and says, "This could be a good thing."

He touches Dean's shoulder. But it's the wrong shoulder -- not the shoulder that once bore Castiel's mark -- and he lingers too long, squeezes a little too hard. He lets Castiel's thumb trace the point of Dean's shirt collar. Castiel's grace churns, something akin to human nausea. Dean narrows his eyes. His muscles tense under Castiel's palm, and he shifts his weight like he means to back away.

"You ain't Cas," Dean says roughly. "You -- who--?"

"Think. I know you find it hard sometimes, but at least give it a try.

A horrible, desperate look crawls across Dean's face. "You -- fuck. Lucifer?"

Smiling, Lucifer says, "Guilty as charged."




Lucifer just sighs when he sees the gun.

"Come on, Sam. You know better than that."




Castiel sharpens his grace into claws and slices into Lucifer's raging light and intent. Lucifer barely acknowledges it, but it delays him for a split-second -- long enough for Dean to skid around the corner at the end of the hall, long enough for Sam to press his bleeding hand to the banishing sigil on the wall.

Lucifer should be above such base, human trickery, but their body -- Castiel's body -- is still tethered to the tatters of Castiel's essence. The connection is thinner than a thread, but it's enough to yank them out of the bunker. They bounce against Metatron's barrier once, twice, three times, then land in a snowy stretch of wasteland Castiel dimly recognizes as northern Siberia. He's exhausted; attacking Lucifer used up all the strength he had. Lucifer's grace shields them from the cold, but Castiel shivers. The howling wind sounds like a scream.

You insignificant little parasite, Lucifer snarls, every speck and mote of his grace churning with furious, unholy wrath. With his mind's eye, Castiel sees a glimpse of Lucifer's true form -- the flaring, architectural sweep of his wings; the shifting animals heads that represent his face, the same beasts bestowed on him by their father, but twisted now, horned and fork-tongued and fanged. God recreated this body for you with his own hands, so I can't expel you. I'd have to carve you out of it piece by piece, and that would leave it too weak to contain me. But if you want to play rough...

The pain is absolute.




Underneath Castiel, Dean writhes and clutches at the sheets. He heaves out a moan that sets Castiel alight, roaring inside him like an unbanked fire.

"Yeah." Dean's back is a long, sinuous line, perfect as it arches, as he pushes back against the thrust of Castiel's hips. "Cas -- Jesus. Just -- just like that. Don't stop."

Castiel wrings his hands at Dean's hips, digging his fingers into Dean's skin nearly hard enough to bruise. He's completely lost to this -- to the needy weight in Dean's voice, to the incendiary heat of Dean's body, to how easily and greedily Dean is taking him in. He's already spent once, after Dean kissed every inch of him from neck to groin, after Dean took him in his mouth, soft and wet and slow. Castiel feels it building again, a dark heat churning in the lowest part of his gut, an electric spark humming beneath his skin.

Dean grabs one of Castiel's hands, tugging Castiel's arm around his waist and urging Castiel to pull them up and back, onto their knees. He slides deeper into Dean, and Dean moans again, shivering. Turning his head, he murmurs against Castiel's jaw, saying --

Castiel jerks back to what's left of his consciousness. In a human form, he'd be gulping for air like a drowning man. His grace rattles around its cramped corner of his body, throbbing with confusion. He hears a low rumble in the distance, something heavier than thunder, deeper than an earthquake.

It's Lucifer. Laughing at him.




He hears Dean's voice.

He hears Dean say his name.




"Give him back you sonofabitch!"

Lucifer pauses for a moment, as if considering it. Then he twists Castiel's mouth into a knife of a smile and says, "Nope. I need him."

Through Lucifer's eyes, Castiel sees the interior of a warehouse. Grease stains spot the worn, concrete floor, and the peak of the vaulted ceiling is lost to shadow. Crowley is unconscious, his legs bent at bad angles beneath a table strewn with the trappings of a summoning spell. Sam is slumped beside him and breathing raggedly. Dean is backed against the dirty wall behind them, pinned in place by Lucifer's grace.

Sam spits a mouthful of blood and asks, "For what?"

"Our father remade this body for him, special delivery. Without him, it would rot faster than my last vessel. So unless you're offering --"

"He isn't," Dean hisses, his jaw tensing as he struggles against Lucifer's hold. "No one is. You ain't hopping in anyone else. The only place you're going is straight back to hell."

"Dean, Dean, Dean," Lucifer says, clucking Castiel's tongue. His grace roils with contempt. "You know what your problem is? You keep thinking you have a choice. Like I said, I need him to keep this body in fighting trim. But I'm a terrible roommate. Sharing with me much longer will kill him."

Dean's head snaps up. His mouth works around something that seems to stick in the back of his throat.

"My grace is considerably stronger than his," Lucifer continues. "Catastrophically stronger, you might say." On the floor, Crowley grunts and leans up on his elbow; Lucifer sends him sprawling again with a flick of his wrist. "My light will consume his eventually. I give him... I don't know. A week? Ten days, tops. Then I'll find some other schlub to roast from the inside out."

Coughing, Crowley stirs again. Somewhere behind Castiel's body, water is dripping, hitting the concrete with a soft plink-plink-plink. Lucifer favors Sam with a cold, expectant look, then heaves out a long sigh.

"I'm disappointed in you, Sam. Think about it: I killed the only person who could open the cage. That means I'm here to stay. How many innocent people do you think I'll burn through, just in your lifetime? How many kitchen witches and depressed teenagers? How many losers like Nick? All because you won't take one for the team."

"Don't listen to him, Sammy."

"And you," Lucifer says, rounding on Dean. He rests Castiel's hand on Dean's throat, a threat veiled in a gentle touch. "Did you hear me when I said Castiel has a week to live?"

Dean's throat flexes and pulls under Castiel's palm. "Yeah, I heard you."

Lucifer gives him the same narrow look he gave Sam, then says, "Huh. I guess you were lying when you told him you --"

"No," Dean cuts in, heat flushing his cheeks. "I never lied to him. Not -- not about that."

Castiel's grace stirs at that, hopeful, but Lucifer quashes it with half a thought, crushing it in a ruthless, invisible fist. Sam spits out another mouthful of blood. Dean clenches his hands at his sides. His mouth opens, then closes, then opens again.

"Cas, I know you're in there. I know you can hear me."

Lucifer snorts out a laugh. "Don't bet on it."

"Cas, please. I don't know why you did this. I don't care." Lucifer gives Dean's throat a warning squeeze, but Dean just coughs and continues. "I just -- I just want you back."

"He really can't hear you," Lucifer says, digging Castiel's thumb into the skin under Dean's jaw. "He's half-dead already."

"Dean," Sam says. He struggles to his knees, but Lucifer flings him back with a lazy shrug.

"Cas," Dean says desperately. His eyes are red and wet; Castiel's grace stirs again. "Cas, you gotta fight him. You gotta throw him out. You -- I need you."

Lucifer tightens the hand around Dean's throat. He curls Castiel's other hand into a fist and slams it into Dean's jaw.

"Cas, please."

Lucifer punches him again.


Castiel forces his grace to coalesce and sharpen, ripping and shredding at Lucifer with everything he has. He feels like a moth flying against a hurricane wind, but he hardens himself, shaping himself into teeth and claws. Lucifer rages at him, engulfing him in pain. It's bottomless, endless, leaves Castiel raw.

Stop wasting your time, Castiel. You aren't strong enough.

"Fight him, Cas. I know you're in there. I know you can do it. You gotta -- Cas, please."

Castiel crashes against Lucifer like a wave.

"Cas, you -- I love you. Cas, please."

Castiel hammers at Lucifer again and again and again. Pain slices through him like a knife, but Dean is pulling at him, clutching at the front of his coat. Castiel rallies himself and slams into Lucifer again. Dean's hand twists in Castiel's collar. His knuckles brush the corner Castiel's jaw. Castiel draws himself up, pulling at every last shred of his grace. Something inside him finally gives.

Lucifer pours out of Castiel in a seething, white-hot rush. He reforms above their heads, shrieking as he churns and rattles the warehouse's broken windows. Castiel's knees buckle; he slumps against Dean's chest. Dean sucks in a breath, then wraps his arm around Castiel's waist. He curves his other hand around the back of Castiel's neck.

"I got you," he says quietly, brushing his fingers through Castiel's hair. "I got you."

Rowena steps out of the shadows cloaking the far end the warehouse. She's wearing the same dress she died in. Her eyes burn black as she cuts her palm over the largest copper bowl on the table. Her accented Latin is swallowed by a gout of acrid smoke. The ground starts to shake.

Castiel's grace flutters, already renewing itself, buoyant and hopeful now that Lucifer isn't weighing it down, scorching it alive. Castiel shivers. He leans into Dean and breathes.