so when he meets isaac at the beginning of their senior year, the best word for how he feels about him is "intrigued". once he figures out what's going on with isaac's home situation (it isn't exactly difficult; missing school and showing up the next day trying to conceal a limp is kind of obvious) he starts to see him as an opportunity to have some fun so he befriends isaac and is nice enough to him that isaac actually opens up to him and willingly tells him about his dad's abuse

and one day stiles is just like fuck it and flat out says it, like "why don't you kill him?" and isaac looks at him in shock like "what?" and stiles has the chance to play it off as a joke but he noticed a subtle change come over isaac when he said that, so he takes a gamble and says "i mean it. why don't you kill him? he's made your life fucking miserable, don't you think he deserves to die? if you tell the cops he'll rot in jail, sure, but he'll get to live. that's not fair." and isaac is fidgeting and looking at the ground and stiles is about to write him off when he glances up and mutters "i don't want to end up in the foster system" and well, stiles thinks, maybe isaac isn't a lost cause after all

-

isaac doesn't turn 18 until spring so stiles has until then to sort of groom him so that he won't back out

and when isaac gets bit stiles takes an almost-scientific interest in his transformation: isaac's improved strength; the primal instincts that overtake him during the full moon; how his body heals faster, but it doesn't stop him from hurting when he's thrown down stairs or kicked in the ribs. stiles catalogues these things and lets isaac's anger simmer– lets it build until it can be useful to him.

-

stiles is isaac's only friend, so it doesn't take long for him to catch onto 1) how loyal isaac is and 2) how important stiles is to him, and he uses that to his advantage and for their first target picks out some kid in their geology class named andy and stiles shows isaac this scar on his elbow and is like "see that? that's from when andy pushed me off the slide when we were kids, he's bullied me for ten years i fucking swear" (it's not a total lie– stiles isn't so much the innocent victim he's portrayed himself to be, but the guy has still been a dick to him, and either way what's important is that he does whatever he has to to convince isaac to join him)

so in late november stiles comes up with a plan to lure andy out to the preserve, like maybe he says he's meeting up with some guy to buy pot and inviting andy along is like a peace offering or something

it's their first kill, before they've figured out things like what combination of tools is the most fun and how long it takes a person to bleed out, so it's fast and messy, and afterwards stiles actually does feel like he's on some sort of high, like everything is so incredibly vivid, and he turns to isaac who's all quiet and asks "so, whaddya think?" and isaac says in a hushed voice "it felt… i felt powerful" and stiles realizes that's how he can rope isaac into this for sure, like isaac's always needed to feel like he's in control of something in his life and this is how he can get it afterwards they dump the body in a secluded area of the preserve for scavengers to eat; it's less work that way and even if it does get discovered it's not like anyone's going to suspect a couple of teenage boys

-

they kill one more time in january just for the fun of it. "you got a hit list?" asks stiles. "no," isaac says, "and isn't it better if we pick someone with no connection to us, anyways?" stiles nods approvingly, and they flip to a random page in the phonebook and settle on one 'jamie morgan.' after that they lie low for a while because they don't want to risk getting caught

and as spring draws nearer isaac begins to feel an itch in his fingertips like the claws hovering millimeters below his skin, like he just wants so badly to rip into something, someone, to tear them apart

(stiles considers having them kill isaac's dad on his birthday, making a proper gift out of him with a bow and everything, but it seems like it'd be a little suspicious if anyone figures out isaac's past, so they wait until may.)

-

they're at an abandoned warehouse in the next town over, and the night is warm and when isaac goes to wipe the the sweat from his upper lip he ends up smearing blood across his face. stiles can only imagine how overwhelming the scent must be to his still-new werewolf senses. he's silent the whole time and stiles doesn't push him to talk; they communicate through looks and subtle gestures.

and after mr. lahey's dead, stiles looks up from the trash bag he's stashing his bloody clothes in to see isaac absentmindedly carving a new gash into his father's stomach, and he ambles across the room and says, "you're really gonna dismantle him piece by piece, aren't you." "i'm looking for it…" "for what?" "where is the part… what is it that makes somebody so bad?" isaac has a faraway look in his eyes and stiles knows they're supposed to be on a schedule, they have to dispose of the body and make it back to their respective homes unnoticed in the next couple of hours, but he's never seen anyone as vulnerable as this boy with blood splattered across his face, this boy who flays open skin and severs tendons like he'll find the secrets of the universe beneath them, so he leans in and plants a soft kiss on isaac's lips and sits beside him and waits until he's done.

-

and that's all i got but ldsjlksjdf i need this so bad because it totally starts out with stiles manipulating isaac and telling him there's a reason you got the bite, this is what you were made for but isaac is absolutely not a poor little puppy dog and as it turns out stiles is really just unearthing the potential for darkness and violence he already has in him, and once he realizes that, stiles comes to respect and maybe even love him for it

and idk maybe isaac files a missing persons report but nothing ever comes of it because stiles is familiar enough with the workings of the forensics system to cover their tracks

and after they graduate high school they leave beacon hills for larger city nearby where it's easier to find targets, people on the fringes of society who won't be noticed when they go missing

and they don't kill because of any sense of righteousness or justice but because the rush of power feels so good

and isaac becomes fiercely protective of stiles because he's human and more fragile, like maybe one of their victims wakes up while they're still in the process of tying him down and breaks free and manages to land a punch on stiles before isaac hurls him across the room and brutally murders him ♥‿♥