A/N: This fic is set after Season 3, Part A. I've had this idea in my head since I first saw Sterek intereact and the idea was sharpened as the seasons progressed. I decided to set it after Season 3, Part A because that is where it fits best. I intend for it to be fairly short and sweet - probably about 5 chapters - but my fics have a tendency of getting out of control so we'll see how we go! Enjoy!

Tolerance

Chapter One - The Terrible Idea

It all started with a terrible idea. To be fair, if Stiles had known then what he knew now…well, that idea would have been the best idea he'd ever heard. However, it's only hindsight that's 20/20 (though Stiles did pride himself on his perfect vision, which seemed at such odds with the rest of him) and it all worked out despite Stiles responding with a very clear, firm "No way, dude" when Scott proposed his very terrible idea.

To set the scene: they were standing in a rough imitation of a triangle in Derek's big, creepy loft – the loft that had become the unofficial meeting place for all supernatural powwows since the rest of them either had, you know, parents or, in the case of Isaac, no permanent home to speak of. Derek had been back from his mysterious trip for a week. It had been two since they'd defeated Derek's second psychotic girlfriend and the not-so-Alpha Pack. They were all wondering what the Big Bad Evil was that Deaton had so direly warned them of. At this rate if the Big Bad Evil didn't kill them, the suspense would.

Considering everything that had happened and just who Scott was as a person, it made sense that he proposed what he did, despite how incredibly stupid it was. Scott was the kind of guy that needed to be helping someone, fixing something, even when there was no one to be helped and nothing to be fixed.

He started with, "So I've been thinking…" and ignored Stiles' muttered 'Uh oh'. "It's been two weeks since we sacrificed ourselves to the nemeton and nothing has happened."

"Yeah, so don't jinx it now, buddy!" Stiles replied emphatically, waving his hands erratically to add emphasis.

Scott summarily ignored him again. "And I decided that I'm done waiting around for it to come to us."

"So you want to go to it?" Stiles questioned incredulously as Derek looked on stoically with his arms crossed over his chest.

"What? No. That would be stupid. We don't even know what it is," Scott replied as equally incredulous.

Stiles shrugged self-consciously. "Sorry, seemed like the natural progression of thought," he mumbled, trying to not notice Derek rolling his eyes.

"I was thinking we should prepare for it – whatever it is. You know, increase our strength so when it comes we can defeat it."

"Great," Derek interjected suddenly, speaking for the first time since they'd entered his loft. "Just accept Isaac and the twins into your pack."

Scott rubbed the back of his head sheepishly. "Uh…well, that's not really what I…"

"Okay, so you want me to teach you how to use your Alpha powers."

Scott looked off to the side. "Well, that's not exactly…"

Derek raised his eyebrows, his turn to look incredulous. "Well I can't imagine what else you could do that would possibly help prepare you."

"Short of you becoming part of his pack," Stiles shot out.

Derek turned a familiar glare onto him, one Stiles was almost immune to by now. Almost. "Not going to happen."

"What, so you're perfectly okay with turning teenagers but too proud to follow one?"

Derek's glare intensified. "I don't need to explain myself to a scrawny, pale seventeen-year-old human who is too weak and useless to be more than a badly-clothed mascot cheering from the sidelines."

"Hey, I've done stuff. Things, even! Why, I -"

"Stop!" Scott yelled, eyes flashing red, one step away from turning. "I wasn't going to ask Derek to be a part of my pack, okay? Just drop it. I was going to ask if you two could help me try something."

"I'm all ears, Mr Alpha Wolf," Stiles prompted when Scott paused.

Scott took a deep breath. "I want you to help me build a tolerance to wolfsbane."

He looked at Stiles and Derek expectantly, hopefully, as though anticipating praise for his enlightened idea. What he got was two blank stares, so he filled the increasingly awkward silence with babble.

"I was reading up on how people can become immune to certain poisons if they ingest increasing amounts over time, building a tolerance to it. Then I thought about how much of a pain in the ass wolfsbane is and how much stronger we could be if we could develop tolerance to it. I even checked with Deaton and he said it had never been tried before that he knew of but that it should work…theoretically."

Derek and Stiles exchanged glances, as if checking to see if the other had heard what they themselves had heard. As if that moment of connection wasn't disturbing enough, they soon found themselves in complete agreeance for perhaps the first time ever.

"No way, dude."

"No."

Scott looked unaccountably crestfallen. Stiles found it hard to believe he'd actually thought he and Derek would think this was a good idea.

Stiles opened his mouth to launch into his rant about how terrible this idea was, when he paused and looked at Derek. "Did you want to, or should I? Because I warn you, I might be a while and I might take all of your best argument points and I don't want to hate me," he paused, considering, "more because I'm making you look like you don't have anything to say, though to be honest you generally do a pretty good job of that on your own. Still, I'm just saying -"

"Stiles," Derek growled.

"Okay, okay," Stiles replied, putting his hands up placating, "but remember I did warn you." He turned to Scott, who looked slightly concerned about what he knew was coming his way.

"Firstly, this may have worked on humans, but you're not human. You're a werewolf. You know, freakishly glowing eyes, dirty long claws, spontaneous facial hair. You can't assume things work the same way for you, Scotty."

"But think about it, Stiles. I have an enhanced healing ability. If anything, that should mean it would work better for me. What would take humans years to accomplish may only take me weeks, months!" Scott argued.

"Okay, say you're right about that – how do you know it will actually work at all? We don't even know why wolfsbane is toxic to you guys, only that it is. It just seems like some weird supernatural mojo, not something you can build a tolerance to."

"Maybe you're right, but we won't know for sure unless we try it! And as you keep reminding me, I'm an Alpha now. I'm stronger than I was before. Maybe I can handle it more than I could when I was a beta."

Stiles rubbed his palms over his eyes and through his disheveled hair in frustration. "Yes, Scott, you're an Alpha. And do you remember what happens when you come into contact with wolfsbane? You shift. Uncontrollably. And guess what? This guy," he pointed to Derek, who raised his eyebrows in response, "isn't an Alpha anymore. He can't make you turn back, he can't control you. And there are no more Alphas here, Scott! We got rid of them, remember? No Alphas! No more Alphas!" He abruptly dropped to his knees and looked under the couch they were standing near. "No Alphas here." He stood and did a 360 rotation on the spot. "Can't see any Alphas." He retrieved his wallet from his pants and opened it, peering inside. "No Alphas in here, either. Just a condom that doesn't freaking fit." He took the condom out and threw it on the ground, studiously ignoring Derek's twitch of the lips as he saw the glaring 'XXL'. "But no Alphas! So if you can't control yourself, who the hell is going to, huh?

Scott ignored Stiles' melodramatic antics. "Lock me up. Chain me. Whatever it takes. Derek is just the insurance policy, but hopefully we won't need him to step in."

Stiles rubbed the bridge of his nose. "So you want me to lock you up, expose you to wolfsbane, and keep vigil with Derek in case something goes wrong – which it probably will, by the way, because this is a terrible idea – again and again until you're miraculously immune to it? Am I getting this right?"

Scott looked a little unsure of himself for a too-brief moment before locking his jaw in a stubborn expression Stiles knew all too well. It didn't matter how much logic he and Derek – well, mostly he – threw at Scott, his Alpha best mate wasn't going to change his mind. The best he could hope for was to convince Derek to help, because Scott was going to do it with or without them. And as much as he hated to admit it, they did need Derek. Unless…

"Why Derek? Why not any one of the other betas? Or Allison, or Mr. Argent?"

"I don't trust Peter or the twins."

"Which is probably the smartest thing you've said since we got here," Stiles conceded.

"And Isaac…he's too inexperienced. He too badly wants to be a member of my pack to be able to stand up to me if I lose control. And while Mr. Argent has been really helpful, he's still a hunter at heart and I don't know if he'll be too crash hot on the idea of eliminating one of the only weapons humans have against us."

Stiles silently conceded that these were valid points. "You didn't mention Allison."

Scott's expression closed. "No, I didn't."

"Isaac could help out," he offered.

"No," Scott replied resolutely, his tone leaving no room for argument.

Stiles sighed, knowing exactly why he didn't mention Allison and why he was resistant to the idea of Isaac even helping. Love. Terrible stuff.

"What do you even need me for? As much as I hate to agree with Derek even slightly on this, I am just a pale, scrawny seventeen-year-old human. There's not much I can do to stop you, though I definitely take issue with the badly-clothed comment." He looked down at his battered Nike's, baggy jeans, a band t-shirt so faded he didn't even know what band it was for anymore, and one of his dad's old plaid shirts that sat open over the tee. "Okay, shit, maybe a little bit, but in my defence I was asleep when you called and you did say it was urgent, so clothes weren't really a priority at the time." He glanced over at Derek, who looked perfectly put-together in dark fitted jeans and a fitted grey tank, muscles bulging in all the right places. "Though I have to say I'm now kinda re-evaluating those priorities."

Derek smirked. Stiles narrowed his eyes at him in a pale imitation of Derek's bone-chilling glare.

Scott, ignoring the interplay between the two, shrugged, "It felt pretty urgent at the time. Besides, I need you because what do you do with any scientific experiment?"

"I wouldn't exactly call messing around with supernatural phenomena scientific, but okay, I'll play. You record observations, results."

"And you're really good at that. I know because you have an A average in chemistry and Mr Harris always made comments about how detailed your note-taking is."

"Lydia has, like, an A plus times a thousand but I don't see her standing here."

Scott silently beseeched him with puppy dog brown eyes. "But you're my best friend, Stiles."

As if there was any argument – logical or otherwise – that he could throw against that dirty trick. "Okay, fine. Fine. I'll help you."

Scott beamed at Stiles, which caused Stiles to shake his head at the blatant manipulation of his loyalty, before Scott turned to Derek with a hopeful expression.

Before he could even get a word out, Derek spoke. "No."

"But -"

"No. Too much risk for too little reward."

Scott's eye bugged out. "Too little reward? If this works, you could be immune to wolfsbane!"

"Ifit works, which Stiles already pointed out is highly unlikely. And why should I risk my neck stopping you when you inevitably get out of your bindings?"

"Don't think you can take him, Mr Big Bad Wolf?" Stiles challenged.

Derek glared at him, causing Stiles to flinch despite his best intentions. Derek smirked. "No, I just don't see why I would put myself to such an inconvenience. Not to mention all the nights you want me to be playing guard dog."

Scott put his hands up placatingly, "But it would only be two nights a week! Deaton said my body would need a few days to expel all the wolfsbane in between doses."

"Two nights a week I could be doing anything else, and literally anything else would be preferable to sitting around with this guy," he nodded his head in Stiles' direction, "waiting for you to either go on a murderous rampage or die."

"Literally anything else, Derek? Or figuratively?" Stiles questioned with a deceptively innocent tone. "Because I can think of some literal things that you'd probably rather not be doing, though there's no accounting for taste…" he looked Derek up and down, as though he was looking at him with a new perspective. "And by the looks of you, Big Guy, you could be into some pretty freaky shit."

He noticed his too-large condom laying on the floor between them, picked it up, and threw it at Derek, who automatically snatched it out of the air without breaking his gaze from Stiles'. Stiles swallowed deeply at the easy display of effortless grace and Derek's light eyes burning into his. As always, he covered discomfort with bluster. "Make sure you bring protection. You know, if it fits."

Stiles braced himself for the full brunt of Derek's displeasure, but what he got instead was a slow smile that heated the blood in his veins.

"Oh, it fits."

Stiles' body flushed all over and he tried to calm the blood pulsating heavily and rapidly through his veins, all too aware Derek's werewolf senses could pick up on the sound of his reaction. He only hoped the werewolf chalked it up to anger and not…anything else.

Scott had watched the exchange with confusion, having only had a couple of occasions to see Derek and Stiles in action. It dawned on him that they were probably always like this and perhaps forcing them together for two nights a week for the foreseeable future was riskier than him taking wolfsbane. However, it was too late to back out now and he'd just have to deal with the consequences of his experiment, whatever they turned out to be. Besides, it would all come to naught anyway if Derek refused to help.

"Stiles," Scott ground out meaningfully.

Stiles rolled his eyes at Scott then looked at Derek with a too-innocent smile. Derek immediately narrowed his eyes in suspicion. Stiles, smile straining, swept his arms to the side. "Derek, come step into my office for a minute."

Derek raised his brows for the tenth time that evening. "This is my loft."

Stiles' smile failed and his arms dropped to his sides. "I know, Derek, it was a figure of speech." He sighed in exaggerated frustration. "Just…come over here for a second, okay?"

Derek sighed his acceptance and followed Stiles over to the back corner of the main floor area of his loft. It was an almost imperceptible movement, but Stiles noticed Derek's sleight of hand as he slipped the XXL condom Stiles had thrown at him into his pocket. Stiles' eyes bugged.

So it actuallydoes fit?He glanced at Derek, who was walking just behind him, then glanced down at himself. Actually, that kind of makes sense. All things in proportion, I suppose. But, wait. Does that mean he's actually going to use it? But with who? Psycho Girlfriend Number Two is dead. Maybe there's someone else. Maybe he's going to use it tonight!He didn't know why that last, somewhat illogical thought made him squirm in discomfort and was about to examine the feeling further when he felt Derek's glare on the back of his neck and realized they'd reached the other side of the room. He shook his head clear. Maybe I should focus and stop thinking about Derek's sex life.

And just not think about Derek's sex life ever.

"Okay, so obviously we both agree this is a terrible idea, which is slightly terrifying because we generally don't agree on much." He paused. "If anything."

Derek scoffed. "You're telling me. I thought it was your job in Scott's pack to come up with the terrible ideas."

Stiles' mouth gaped open and he was speechless for all of five seconds. "Me? Me with the terrible ideas? I happen to recall some of my ideas saving lives, thank you very much. I'm the idea guy. That's my role. That's what I do. If anyone has a history of terrible ideas, it's you."

"Excuse me?" It was more of a threat than a question, but Stiles decided to take it as the latter.

"Well, let's examine where you are in life right now, Big Guy." He raised his hands and started ticking off items with his fingers. "You decided turning teenagers into werewolves was a good idea, but two of them are dead and the other isn't even in your pack anymore. You didn't burn your sociopathic uncle into dust, so now he's back from the dead. Which is awesome, by the way, because we can all agree he's such a swell guy. You don't have a pack, you're no longer an Alpha so you can't make another one – small favors and all that, I suppose – and even your sister is mysteriously gone. And you've dated two psychotic women to date, unless there's a couple more psycho skeletons in your closet - or under your bed, wherever you bury them - that I don't know about. I dunno, Derek, either you're the most unlucky guy who's ever lived or you make really bad decisions. I find it hard to believe anyone could be that unlucky, so I'm inclined to go with the bad decisions."

Over by the window Scott put his head in his hands and accepted the inevitability that Derek was never going to help him now.

Derek narrowed his eyes at Stiles and crossed his arms over his chest. "I don't need to justify myself to a runt like you, but yes. I openly admit I haven't always made the best decisions, but maybe you try having this much power and responsibility and see how you fare before throwing stones. Something tells me you don't think you'd do such a crash-hot job, or is there another reason why you turned Peter down and haven't asked Scott to turn you, despite bemoaning your fragility ever chance you get?"

Stiles found himself speechless for the second time in five minutes, a feat he didn't think anyone else had ever managed to accomplish. He hadn't known Derek knew so many words, or that he could string sentences together – accusatory, more-accurate-than-he-was-comfortable-with sentences. It was only fair, though, after everything Stiles had dished out at him; things that had been brewing under the surface and had probably needed to be said before he could work with him as a team on anything. Uncomfortable, yes, but now the air had been somewhat cleared…

"Okay. So are you going to help us?"

He heard Scott's groan from the other side of the room.

"Why, because you made such a compelling case?" Derek replied sarcastically. Stiles hadn't known Derek could do sarcasm either. He was learning all sorts of new things today - Derek was more perceptive than Stiles had ever given him credit for, he could speak more than five words at a time, he had an extra-extra-large penis…

Wait, what? Don't go there, Stiles! Distraction – quick!

"Well, we make a great team…" he clicked his fingers excitedly as he remembered something. "Even Matt the Mass Murderer said so!"

"I thought he said you make a great pair," Scott called out from the other side of the room.

Stiles spun around and glared at the shadow in front of the window. "Scott, what did I tell you about my office?"

"Once you step inside it, I can't hear you anymore," Scott repeated morosely.

"That's right. And even if you can hear me?"

"Pretend I can't."

"Okay, thank you. The door is now closed again."

He turned back to Derek with an apologetic shrug that Derek immediately ignored. "Why do you think reminding me of one of the most unpleasant experiences of my life will convince me to help you?"

"Unpleasant? Unpleasant?" Stiles repeated indignantly. "I will grant you that being paralyzed from the neck down for an extended period of time isn't exactly pleasant, and I suppose you do make a bit of an uncomfortable mattress." He poked Derek's firm chest, taking note of how little give there was. "Too firm, too lumpy…" he mimicked bulges on his arms with his hands.

"Not what I meant," Derek ground out through clenched teeth. "We don't make a great team, and I certainly wouldn't take a psychopath's word for it."

"Why not? You seem to have an affinity for them."

Derek growled low in his throat and the hairs at the back of Stiles neck stood up. He felt like prey. He tried not to grin.

He didn't quite know why he couldn't help riling Derek up, testing the limits of what he would let Stiles get away with, whenever they were together. Maybe it had something to do with the rush of adrenaline coursing up his spine as they bantered, or the electricity surging through the space between their bodies. Whatever the reason, he'd probably pushed as much as he could for now and he did actually need Derek's help. He knew Scott would be pissed if he screwed this up for him. Still, it was not like he ever meant to do it; it was just some sort of sick compulsion.

"Stiles!" Scott yelled again from the distance.

Stiles sighed exaggeratedly and looked up at Derek. "See what I have to deal with every day? Honestly, the amount of times I've told him…" he trailed off and sighed again. "I hope you're not so difficult to train."

"Train?" Derek growled.

Stiles shivered again. So maybe he wasn't quite done for the night.

"You're right, you're a hopeless case. I won't even try."

"You do realize you're probably further away from convincing me to help you than you were when you started, right?"

Stiles grinned at him. "But it doesn't matter because I know you're going to help us anyway."

Derek raised his eyebrows again, as if to ask 'Oh?'

"That's right, sour wolf. You're going to help us because despite what you've so grumpily proclaimed, you're too curious about the idea of wolfsbane immunity to not help. Plus, you know Scott and I are going to do it with or without your help and we have a much lower chance of destroying the entire town if you're on hand as – how did you put it? – oh yeah, as our guard dog." He smiled smugly and crossed his arms over his chest, though sadly it didn't quite look as intimidating as Derek's stance. "You want us to go through this charade of trying to convince you because you like the idea of Scott begging you for help after refusing it so many times in the past. Am I right?" He leaned forward and dropped his voice into a stage whisper. "That question was rhetorical, by the way."

Derek surprised him for the fourth time that night by smirking in response. "Thanks for playing, Stilinski. It's been entertaining, if not slightly disturbing." He turned to Scott. "Be here tomorrow night at seven, and bring your little sidekick with you." He turned back to Stiles, who was sputtering 'sidekick' in increasingly indignant tones. "Now get out," he stated coldly before walking away in the direction of the balcony, leaving Stiles feeling uncomfortably destitute yet undoubtedly anticipating the nights to come.