He doesn't know why he's so surprised, really. Derek's been coming by a lot, and not just to make sure he hasn't ended up getting pod-peopled again. He hounds Stiles about his homework, bitches about his taste in music, reads comics when he thinks Stiles isn't looking. It's almost comfortable. He guesses he just wasn't thinking past that. He's been doing a lot of that lately, actually going out of his way to not think about what things mean. But mattering to someone else isn't something he's ever been good at registering. Really, his entire life and self-value are more or less defined by what he does for other people. Without Stiles, his dad would just work forever and eat nothing but double-bacon-bypass-burgers and be dead of a heart attack by fifty. Without Stiles, Scott would never have gone out for lacrosse, would never have passed eighth grade English, would never have gone into the preserve and ended up a werewolf... okay, maybe that's a bad example. But he's nearly positive that without him, Derek would forget what it's like to be human, and that's not okay. It's good that he matters. It is.

"I already have you on speed dial," Stiles answers brightly, holding up his phone and showing Derek the illuminated screen. Number two, right next to his dad's cell. It says something about how important the older man has become. Or maybe just about how much trouble Stiles gets into. "So, no worries, right? Except all the worries. You know what I mean. I'll call if anything shows up. Or if anything weird happens. Or... you know." He stops his babbling with an effort, knowing if he starts now he's never going to be able to stay cool for Scott, and that's important for making this work.