This starts towards the end of the episode Wolf's Bane and goes AU from there.
Aconitum
Get out of there right now Stiles! He's the Alpha! Peter is the Alpha!
Peter Hale.
The Alpha was Peter Fucking Hale. The guy who was a vegetable in a wheelchair. A vindictive, blood-thirsty werewolf vegetable in a wheelchair. Derek's own flesh and blood. His only living relative left.
Peter killed Laura Hale. Jesus Christ, if that wasn't messed up! He ordered Scott to kill him and their friends, even ran Derek through with his own claws... and was now beating the ever living shit out of him.
Stiles stumbled on the edge of the sidewalk, foot landing awkwardly as it hit the asphalt, turning an odd angle. Pain shot up his leg like a short burst of electricity. "Crap," he hissed, falling against the front of his jeep. He pressed his weight down of it, testing it, the pain not as intense as before.
Get out of the way. Derek was fighting to protect Stiles - Scott's pack member, not his. Stiles had no ties to Derek. Hell, Stiles was a huge reason he was now a wanted criminal. All Derek saw in Stiles was some annoying kid attached to an equally annoying, love sick werewolf who he felt he was somehow responsible for. Stiles was just an unnecessary accessory.
Yet, Derek threw himself at his uncle - an Alpha. No hesitation, he just did it - for Stiles.
"Holy crap," Stiles' breath was visible in front of him. He's going to kill him. His uncle is going to kill him. Why wouldn't he? Derek attacked his own family, no questions asked, and to protect an enemy. As a complication regarding Scott, Stiles was a problem that needed to be nipped in the bud.
"Dammit!"He stood there, head bowed. Stiles slammed his hands down on the hood, fingernails digging into his palms. "I can't just leave him in there!" But what could he do? He couldn't make it out of a scrap with a chihuahua. How the hell was he going to go toe to toe with an Alpha Werewolf?
He should get help. But Scott was in the middle of the lacrosse game… and, oh dear God in Heaven, was his father going to tear him a new one…
Focus Stilinski.
Scott wouldn't make it in time, werewolf speed or not. Derek would be bloodied and probably dead by then, and Peter would be off frolicking under the moon.
Getting the Argents would get everyone - including Scott - killed.
And calling the authorities would be laughable.
That just left him.
Stiles scrubbed his hands through his hair, pacing the length of his car. "What should I do? What should I do!"
He was useless. Charging in there would be more idiotic than just leaving. Derek would have to fight to keep Stiles and himself safe. Helping would be more trouble for Derek than it could be worth. He should just hop into his Jeep, go to the school, and get Scott. Hope and pray that Derek pulled through.
Still... It wouldn't be right. He couldn't just ditch the guy to save his own skin.
Derek didn't ditch him. No matter how much he hated Stiles.
Don't fight because you have to. Fight because you believe it's something worth fighting for.
His mother said reminded him shortly before she died. She had always told Stiles to do something because he believed it was worth doing - even if it meant detention. Dad wasn't completely on board of that bandwagon like her, but Stiles had grown up believing in it.
He didn't like Derek. He was a terrifying asshole who enjoyed inflicting him pain. Stiles didn't trust him as far as he could throw him. And that wasn't very far.
Derek risked his life to save him, and that was something worth fighting for.
Hell. Stiles had fought for less.
God bless Scott for working in an animal clinic. He couldn't have found a more perfect weapon.
Stiles practically tore his Jeep apart looking for effective weapons. His lacrosse stick, helmet, a lighter, an almost empty bottle of car oil and four tennis balls were the best he could find. He was about to learn just how effective MacGyver would be against an Alpha.
But, he found a dog whistle in his glove compartment - obviously a gift from above.
With the whistle in his front jean pocket and lacrosse stick in hand, Stiles slowly entered the eerily empty building. He held the stick like a shield. It was quiet - no sign of life anywhere. No nurses, patients, anything. He couldn't even hear the sound of hospital machines.
What the hell did Peter and that psycho bitch nurse do to this place?
The lights were almost too bright as Stiles made his way back to Peter's room. The sign of a fight was obvious. Walls were dented and the plaster from the roof littered the floor. The nurse's desk was all but demolished, paper and office supplies scattered about the floor. He pocketed a pair of scissors as he passed by, shoving them into the back pocket of his jeans.
Psycho bitch was still unconscious on the floor. Good, - she deserved to get elbowed right in her bitchy face.
He could hear muffled voices coming from a curtained off area behind the nurse's station. Stiles took a long breath. It's now or never. The two probably had already noticed he was there by now, stupid heightened senses. But he figured out a trick - at least with Scott. The more you hesitate, the more time they have to prepare for an attack. But if you just charge them, you can catch them off guard.
Well, you can catch Scott off guard. But that counts for all werewolves to... right?
Shit. Shit. Shit.
Stiles didn't wait. He didn't eavesdrop on the two. He barreled through the room, lacrosse stick armed behind him like a bat. Peter towered above Derek, the younger pinned to the ground, injured and blood dripping from his mouth and stomach. Blue eyes that had been locked with red now broke contact.
"Stiles! No!"
It didn't matter. Peter had his entire attention solely on Derek, grinning down at him with a superior look in his eyes, the devilish sneer in place just for his nephew. As those smug eyes finally shifted toward him, smirk turning down, Stiles was right beside him, sending the lacrosse stick straight into his gut with all the strength he had.
It was like hitting a brick wall. Stiles arms shook from the force. He could hear the plastic pole crack. Peter grunted as he hunched forward. He seemed more alarmed than in pain, looking at the lacrosse stick like it appeared out of thin air.
The look was gone instantaneously. His eyes became sharp, hand striking out like a snake and latching onto Stiles' stick. He let go immediately, expecting Peter's move. Stepping back from the man, he watched in awe-stricken horror as Peter broke the stick in half. The bottom dropped to the floor, rolling away while the top was thrown to the other side of the room.
"That," Peter addressed him calmly though his eyes glowed red, "…was an incredibly stupid thing to do."
Stiles met those eyes, even though that was probably more foolish than brandishing a piece of flimsy sporting equipment. He could feel his heart race, knowing the two wolves could hear it too. His voice, however, did not waver. "Hard to believe, but.. this isn't the stupidest thing I've done."
"Stiles," Derek was rising to his knees, teeth clenched in pain.
The older man rolled his shoulders, turning himself toward Stiles. "Of that, I have no doubt." Stiles was surprised see the expression change on the Alpha's face - the hardness melted into something of genuine interest. He was a human that would strike him, knowing that it would be useless. A smile tugged at the corner of his mouth, intrigued red eyes roaming over Stiles.
"Stiles! Get out of here! Now!" Derek commanded. The sheer panic in his voice drove Stiles into movement, reaching into his pocket for the whistle. Peter advanced, backing Stiles into the cabinets across the wall. Stiles fingers curled around the small metal.
"Derek, cover your ears!" He didn't look to see if the wolf did it. He crouched forward, curling into himself and protecting the whistle from the advancing Alpha. Peter saw it. With a snarl, the man grabbed at the back of Stiles jacket and jerked him upward, clawed hand wrapping around his wrist.
The whistle was already to his lips. Before Peter could take it, Stile blew.
Stiles couldn't hear a thing. Peter and Derek however, could hear it crystal clear. Peter howled, throwing Stiles to the side, covering his ears. He stumbled, but somehow managed to keep his balance. He took another breath and blew harder, aiming the instrument right at the Alpha. Stiles watched as the older man fell to his knees. He let out a low, inhuman whine. Hands shaking as the claws retracted back into normal fingernails.
Stiles paused, looking to Derek. He had two fingers buried deeply into each ear, but his face was scrunched up, breath coming through his clenched teeth. "Let's get out of here before he can recover," Stiles yelled, running towards him, whistle held close to his mouth and keeping his eyes on Peter. "Do you need help up?"
Like lightening, Derek's hand was on his wrist, jerking it back from his mouth and twisting. Stiles cried out, the spasm in his fingers causing him to drop the whistle. "The hell?" Stiles choked, his skin pinching underneath the Derek's grasp. "Derek, what are you doing?!"
Derek had the decency to look upset. "Stiles, don't worry about me and just get out of here. Please. I'm not in any danger-"
"Yeah, the huge gash on your chest is proof of that!"
"This is none of your business." Derek growled. That was enough to make Stiles stop. "You have no idea what you have just done."
A low growl made them both turn. Peter was now standing back towards them. He was looking at his palms. Small droplets of blood stained his palms. Blood ran down his ear onto his neck. The Alpha whipped his head towards them, bright red eyes locking on Stiles. "You little bastard..."
Peter looked as if he were about to lunge forward when Derek pushed Stiles behind him. Peter snarled.
"I let you by with protecting him once, Derek." His eyes glowed as they locked with his nephew. "Do not be foolish enough to think I will allow it again. Now, step aside."
"No," Derek growled. He pressed Stiles backward, crowding him as far back as they could go.
Peter fangs grew as he flashed a nasty smile. Stiles grabbed at Derek's jacket, fingers curling into the fabric. "Is he really worth defying me? Your Alpha?"
Stiles froze. Peter was Derek's Alpha too.
Derek paused. "He's the sheriff's son."
Peter raised an uninterested eyebrow. "And?"
"The police are already paranoid with all the murders happening. If anything happens to him, it will become personal vendetta, and they will be impossible to deal with. This will just complicate things."
Peter smiled knowingly at Derek. "You're lying."
"Actually, he's not," Stiles piped up, leaning to the side of Derek's left shoulder. "Sheriff Donald Stilinski is, in fact, my father. I have photos, videos, and a really annoyed voice mail from Tuesday to prove it." The two wolves ignored him. Peter kept his gaze on Derek, who was practically vibrating in front of him.
"If you hurt him, I will never help you." Derek stated. "Am I lying now?"
" Wait. Rewind. Help? Help with what? " Stiles interjected. He pushed out from behind Derek. "What do you mean help? You mean with the murders? You can't!"
"Stiles..." Derek growled.
"He killed all of those people! He ran you through with his own claws and left you to die! He bit Scott, and then tried to get him to kill me and the others! Hell, he probably killed your-"
Suddenly his back was slammed into the floor, teeth rattling from the impact. Derek leaned over him, his blue eyes flashing. Stiles opened his mouth to shout, but Derek's hand covered him, gripping his jaw painfully.
"Stiles, if you know what's good for you, you will shut the fuck up." Stiles frowned up at him, fingers gripping the hand on his mouth. Derek chest rose dramatically, moving with each heavy breath he took. His nostrils flared. As his blue eyes stared down into his, Stiles could see something past the glare.
Holy shit, Derek is actually scared right now. The realization hit him like a brick. He was scared of Peter Hale, of what the man could do. Because, when push comes to shove, Derek can't say no to his Alpha. If Peter ordered Derek to move, or even kill Stiles himself, Derek would have to do it - whether he liked it or not.
He saw what Peter did to Scott. If it weren't for Allison, they would have been dead.
Derek didn't have that kind of trigger.
Stiles nodded slowly, not looking away from Derek's eyes. Stiles gave Derek a small, understanding nod. Derek nodded back. He seemed relieved as his shoulders deflated. He removed his hand from Stiles mouth.
Peter laughed, causing Stiles to stiffen on the floor. For a moment, he forgot the man was still there. "Now I get it. You claimed yourself a little pet, didn't you?"
Stiles felt his brain shut down. He stared dumbly at Peter, then to Derek, mouth gape open like a fish.
Pet. Pet. Pet. PETPETPETPET OH DEAR GOD.
Stiles scrambled up from the floor, trying to back away from Derek, but his hand latched onto Stiles' forearm before he could escape.
"Yes." Derek looked at Stiles as he spoke, his eyes staring daggers at him. Stiles stopped moving, returning the same glare."I have not, officially, claimed him, but he is mine."
"The fuck I am!" Stiles yelled as Derek's hand quickly clamped back over his mouth.
"That means you can't harm him in any way." Derek stared down his uncle.
"Derek, Derek," Peter sighed, shaking his head as though he were dealing with a toddler. "I am the Alpha now. He may be 'yours'," his fingers made quote marks in the air, his smiled widening. "But as pack leader, it makes him 'mine' as well."
A sick, cold feeling formed in Stiles' stomach.
No no no no nonono, this was getting way out of hand.
He wasn't Derek's, and he sure as hell wasn't going to be Peter's - that's just… no. Stiles' breath began to quicken, turning into sharp, short gasps from under Derek's hand. He squeezed his eyes shut. He couldn't be having a panic attack.
God, not now.
"Uncle," Derek's voice snapped Stiles out of it. The stricken, almost frantic, tone anchored him back. Stiles looked at him, seeing actual concern on Derek's face. "I will help you I will do anything you ask, just... don't hurt him. Please."
Derek said please. Holy fuck, what kind of hold did Peter have on Derek?
What did he miss while he was outside?
Peter stared Derek down, eyes darkening as he studied his nephew. Stiles looked too; really look. Derek had his head bowed, neck tilted to the side. Blue veins were prominent, laid out in front of Peter. Stiles eyes widened. Derek was submitting to Peter.
Derek was submitting to Peter - for Stiles.
Stiles really should have just left and gotten Scott.