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There's someone in his loft.
Derek pauses outside his door, head cocked, listening inside. One heartbeat, steady and calm, probably near the window. No shuffling, no movement of any kind.
Someone waiting on him, then. Derek shoves the door open, shifts and charges inside, but stops mid-step when he realizes that it's just Stiles, back to him, staring out the window like he hadn't even heard Derek's aborted attack.
"What are you doing here?" Derek asks gruffly, trying to hide his embarrassment about nearly tearing into Scott's best friend. He shifts back, but as he does, he notices a strange smell in his loft. Something...
He can't quite place it, but it's cloying in the back of his throat.
Stiles still hasn't answered, hasn't moved, and the hairs on the back of Derek's neck rise. Stiles is never this still; he's a constant blur of motion and words and nervous energy. Derek is shocked at how wrong he seems without it.
He's surprised by the broad sweep of Stiles's shoulders, at the definition under his single t-shirt that was never hinted at under his flannel and hoodies. Taking away the layers should have diminished him, but instead Derek is realizing that perhaps Stiles isn't as breakable as he pretends.
"Stiles," Derek repeats after a moment, because the silence and lack of movement are becoming creepy, and he takes the final few striding steps to rest his hand on Stiles' shoulder.
He doesn't examine the impulse to touch too closely.
Just before he makes contact, Stiles moves, whip-fast, turning on his heel to face Derek. Finally, motion from him, but it's all tightness and control and not at all like Stiles.
Nervous energy begins to coil within him.
"This is a safe place," Stiles says, and the off-ness extends even to his voice, which is colder and flatter than Derek has ever heard him. "Isn't it?"
"Not from teenaged werewolves throwing raves," Derek says, hoping that levity will cut through the chill in Stiles' expression and allow the boy he knows to shine through.
"Or for teenaged werewolves themselves," Stiles says, reaching out and thoughtfully running a finger down the outside of Derek's hand, resting his fingertip on Derek's entirely human fingernail.
Derek closes his eyes tightly, trying to exorcise the memory of the way Boyd's skin gave way under his claws. But with it came the memory of Stiles' hand on his shoulder, pulling him away from the abyss, and the nervous energy settles into something deadlier.
"Humans need to watch out, too," he says tightly, because this definitely isn't the Stiles he knows. Everything is wrong: the tone, the body language, and -- now that Derek is paying attention -- even the scent.
Stiles briefly flashes a bladed smile. "Threats aren't why I'm here."
"Then why are you?" Derek's never been one to fight with words; that's always been Peter's territory. He half-wishes that Peter was here now, but something deep within him knows that the combination of whatever this is masquerading as Stiles and Peter would be deadly.
"Equal parts appeasement and threat, to be honest," Stiles says thoughtfully.
"I don't understand," Derek says, eyes never leaving Stiles. It's something his mother used to do, feign not understanding until she got handed all the information she wanted. And he wants to know if Stiles is anywhere in there.
Watching this Stiles is hypnotizing. His body is coiled tight as a snake about to strike, and his eyes are empty, and every instinct Derek has is telling him to go for the throat.
To eliminate the threat.
But he can't do that, no matter how much he wants to let the shift take over and let the wolf handle things the way it wants. No matter how much his teeth want to sink into that vulnerable, pale skin just below his jaw.
"I want to be here." Stiles lifts his hand, lets it hover briefly in the air between them like he wants to reach out and touch Derek's arm, then drops it again. "And I don't want to hurt you."
"Then don't," Derek says. "Leave him alone."
He almost wishes he'd bitten back the words in time. He's just given whatever is controlling Stiles ammunition against him; he might as well have handed him wolfsbane.
"Him?" A tilt of the head, Stiles' face twisted into a visage of innocence. "Me, you mean."
Derek doesn't press it; he knows well enough when he's not going to get an answer. Instead he lets his eyes go wolf, and tries to see what's taken over Stiles.
A flash of something dark, and then Stiles' hand is wrapped around his neck. Derek hadn't even seen him move; there was no way it had been human speed. The expression on Stiles' face is deadly and grim, and Derek can feel his fingers digging into his throat.
His breathing is constricted, but Derek tries to stay calm. Stiles is human, no matter what passenger he carries, and he cannot kill a werewolf barehanded. Derek knows he could break him, knows he could shift now. He could tear away those vice-like fingers with his claws, he could snarl and bite and tear with his teeth.
Normally the worst he could convince himself to do would be to reduce Stiles down to a scared little boy, but he can't scare whatever's possessing Stiles. He could reduce it down to meat, but Derek can't. Not if it means sacrificing Stiles.
He can't.
"Aren't you going to fight back, little wolf?" There's something sly and terrible in Stiles' voice now, dark hidden knowledge that uses Stiles' tenuous grasp on morality to try to instill doubt.
Derek has to do something, so he suddenly yanks himself back, hoping to throw Stiles off-balance. Hoping to loosen the grip on his neck, to allow air back into his lungs.
It only partially works; Stiles' fingers scrape into Derek's neck, but he keeps his balance, and all Derek gets for his trouble is a raking set of bruises on his neck, bruises that will fade in moments. His hand slips, just enough for Derek to take in a deep, steadying breath.
It gives Derek the clarity to do something unexpected. Not trusting himself not to break fragile human bones if he removes the hand by force, he advances, hoping to shake Stiles free before he can regain his grip. It works; Stiles ends up with his shoulders pressed tight against the window with his arm trapped between them, the angle too awkward for his human wrist to recover its strong grip on Derek's throat. It puts them face-to-face, with Derek staring straight into his eyes.
Funny how he didn't notice before that they're the same height. Stiles is lean and awkward; he somehow gives the impression of being much smaller than he is, more a force of personality than anything else. But this Stiles is undeniably a threat. Take away the flailing limbs and loud mouth, and this Stiles is nothing but cold, focused control. Everything is deadly still and dangerous, from his squared shoulders to the tilt of his head, and it sets Derek on edge.
Stiles' arm moves, and Derek growls, a low rumble that reverberates in his throat. He reaches up to grab Stiles' wrist before he can re-grip Derek's throat.
He can feel the bones and tendons in Stiles' arm, and it takes more effort than he's proud of to refrain from digging in his claws, from feeling warm fresh blood spilling over his fingers.
He's dangerously close to losing control of himself, barely keeping his human visage in place.
"Is this all you've got?" Stiles tilts his head back, eyeing Derek. His voice is all challenge, a needling tone designed to make him react, and Derek tries to stay steady. Tries to anchor himself, remind himself that he can't do anything.
His teeth sharpen, and he leans in dangerously close to say, "You should leave."
He doesn't know if he's just asking him to go or if he's talking to the thing controlling Stiles. All he knows is that the heartbeat is starting to speed up slightly, and Derek feels his teeth elongate in response.
"Make me," Stiles says. There's no mistaking the tone.
He pins Stiles' arm to the window above his head, putting a knee between Stiles' legs. It's a thoughtless move, something designed to give him more leverage, more balance, but all it does is put him so close that he can feel Stiles' body heat against his, smell Stiles' particular scent, that heady mix of teenage lust and soap-sweat-sunshine.
If Derek just closes his eyes...
If he closes his eyes right now, he could forget the soulless fathoms of Stiles' eyes and could pretend this is real. That he could press his hips forward, that he could nuzzle against Stiles' throat, hear his heartbeat race even as his breath caught in his throat, could taste his pale freckled skin and kiss the translucent shell of his ear.
He could take, could indulge in something simple and happy. Could lick and suck and bite his way to forgetting the bad things in his life.
Could have something here, now, that wouldn't stab him in the back come morning.
But this isn't Stiles . There's something dark and terrible in Stiles right now, and Derek can't do anything to change that. Doesn't know how to help him.
All Derek can do is pin him here and snarl at him like he's capable of hurting Stiles.
Stiles moves, cants his hips just right so that Derek can feel as well as smell his arousal, then rolls them against Derek, a move so brazenly sexual that Derek almost lets go of him. Almost flees the room, because he's losing his grasp on his humanity by the second and he doesn't know what his wolf might do.
The animal side isn't as concerned with morality as Derek is, isn't as worried about the fact that something is using Stiles, and that Derek refuses to use him too.
"You can smell how much he wants you." The voice is low and dark, utterly unlike Stiles.
It's the first time that the thing speaking through Stiles' mouth has explicitly acknowledged that it isn't Stiles, that it knows what Stiles was thinking. That it's using Stiles' reaction to Derek.
It's too much. Derek wants it gone. "Does Scott know?"
"That Stiles has a hard-on for you?" Stiles' free hand creeps around to tug on Derek's belt.
"That you've hijacked Stiles," Derek manages. His voice is a rumble, barely human. He pulls Stiles' hand away from his belt, and his claws bite into the skin.
The scent of blood is the tipping point; it's all it takes for Derek to lose the battle with his wolf. His vision goes red and he snarls. His fangs are grazing against the skin of Stiles' throat when Stiles lets out a panicked whimper, and his heartbeat spikes.
Derek manages to stop himself before ripping out his throat; he ends up with his teeth against Stiles' jugular, mouth hot against skin that's softer than he thought it would be. More delicate.
"Wha-- What's going on?" Stiles sounds so lost. Derek can't help mouthing a quick rough kiss against Stiles' neck as he pulls away, hopes Stiles won't realize. It might be his only opportunity.
He lets go of Stiles' arm and steps quickly back. He doesn't realize how hot Stiles was pressed against him until he feels the chill of his loft.
"You're possessed," Derek says roughly.
"So you tried to rip out my freaking throat?" Stiles demands. His cheeks are flushed, and whether that's from fear or lust, Derek can't tell.
Doesn't have the right to tell.
"You should go," Derek says. "To Deaton, or to Scott. I'll tell them what I saw."
"What did you see?" It's definitely fear now, but not of what Derek had done. Stiles looks terrified, like he's afraid that he's going to find blood and gravedirt under his nails. It doesn't look like a new fear, it looks like he's had time to wonder. Think about the possibilities. Like he's lost time before.
"Darkness," Derek tells him, unable to sugarcoat it. He's suddenly, deeply exhausted.
Stiles nods slowly, like he was expecting that answer. "I'll tell Scott."
He rubs his wrist thoughtlessly, smearing the blood over his pale skin. "Did I... Did it... hurt you?"
Derek shakes his head, not trusting himself to speak of it.
Stiles stares at the blood on his hand, wiping it quickly on the hem of his white t-shirt. "I'll go."
Derek watches him leave, the image of Stiles' blood and those empty, shadowed eyes haunting him just as much as the feel of Stiles' body pressed up against his.
He doesn't sleep that night.