Stiles doesn't bother knocking. He knows Derek's heard him drive up, so he just taps the door open. "Hey, is Scott—" He sticks his head around the corner and jumps, because there's Derek, sitting in the living room, tending to what looks like a seriously ugly cut splitting the skin behind his right shoulder. Derek barely spares him a glance before returning to the task at hand, and Stiles wheels backward until he bumps into the stairs. "—whoa there, sorry, didn't know you were, y'know…"

"Pulled some stitches. Replacing them. Scott and Isaac aren't here yet." He dips the needle down.

Derek plainly isn't expecting a response, but Stiles watches the painstaking way he manipulates the needle one-handed, the awkward angle of the operation, and it's not until Derek freezes and looks up at him that he realizes he's crossed the room and is hovering. Crap. Um um— "Isn't that…hard?"

Derek appears to struggle momentarily for a response; his eyes flick back down to the cut, and he slides the needle through again. "It's fine."

"Doesn't it hurt?"

"It's fine."

"Are you even left-handed?"

Derek grits his teeth, a soft imitation of the fangs-bared ferocity Stiles last saw about sixteen hours ago, during the whole kanima fiasco. "You know what would make this whole thing a lot easier?"

"Hm?"

"If I didn't have to answer stupid questions every two seconds."

Stupid questions.

Stiles decides to go four for four. "Want me to do it?"

Derek pulls the thread taut a little too hard, and Stiles catches the tiny intake of breath before he's back to glaring mode. "You know how to do stitches."

Sardonic incredulity drips from his words like kanima venom, but Stiles is paralyzed only for a moment, because it's dumb for Derek to be doing this by himself when Stiles could probably do it twice as fast and a lot less sloppily. "Well, for your information, as we all know, I'm a total spaz, and when I was a kid, I was always cracking my skull open or bashing my knees on concrete steps or splitting my chin on a tree branch or, well, you get the idea. Basically, I had to get a lot of stitches. Like, a lot. The knew my mom by name at the emergency room. So I know what stitches look like." He plucks the needle from between Derek's fingers, crouches beside him. "And—wow, you suck at this."

The edges of the cut shift slightly as Derek tenses, defensive. "Stiles. I don't do this very often. I try not to make a habit of fighting things I can't heal from." He glances over his shoulder, then turns back again when the motion pulls at the stitches. "And I can't even see what I'm doing."

"Um, yeah, I can tell." This is gross, if he's being honest, this is really gross, but considering all the blood and guts he's seen in the past few months, it's not enough to scare him off anymore. He dives in without a whole lot of regard for how much it's gonna hurt Derek, because Derek's a badass, so whatever, and he kind of deserves it anyway.

The cut's deep but not long, a slice that rips straight across his shoulderblade, paralleled by three others, all less severe. Kanima claws. Apparently Derek can't shake those off like he can pretty much everything else. Stiles is finished before too long, with a minimum of Derek's blood on his hands, and he inspects his work. Not professional-quality, but it's neat enough. And it looks a lot better than the uneven zig-zags that Derek was working on when he walked in. "Okay. That should be good. And pretty unpullable."

Derek stands and rolls his shoulder. His eyebrows lift in something that could be interpreted as approval. "Stiles."

"Hm?"

"Show me how to do it."

A simple enough request, but for some reason Stiles's brain is having trouble processing what just happened. "How to—"

"Stitches. How to do it right." Derek's impatient, waiting for him to catch up.

"Oh! Yeah." He's still holding the needle and thread, and they feel thick and heavy suddenly, like his fingers are asleep. "Um—but I thought you could heal and stuff, so—"

"Not from everything."

"But you said you don't make a habit of fighting things you—"

"Well, it's starting to look like I don't have much of a choice." Derek stares him down.

Don't have a choice. A common logical fallacy, and Stiles jumps on it without thinking. "Well, technically, you do have a choice, because people always have a choice, but when you say you don't, it's just that the other option seems totally unacceptable to you. So it only looks like you don't have a choice. Like, you could choose to not fight the big scary monsters and just sit alone in your house brooding or writing sad poetry or whatever it is you do all day, or—"

"No I couldn't." Derek turns, standing square to him now, and this isn't the first time it's happened, but Stiles always feels a little intimidated bearing the full brunt of Derek's attention. "I can't just—sit here and watch these things happen. I would never do that."

So you're choosing to do something about it. But Stiles doesn't correct him, because the front door creaks open and Scott's voice drifts into the living room. "Sorry we're late, the skirmish went longer than it was supposed to."

Stiles holds the needle and thread out to Derek. "Okay. I'll teach you."