where Stiles is a fun, whimsical librarian who sets up a community puzzle area, and Derek is this one comment at the bottom of the community "helpful tips" board

And it's not like Derek's a puzzle enthusiast or anything. He mostly just wanders into the library every day, listlessly touching book spines, people-watching out the windows from a study cubicle, not really knowing what he's doing with his life or why he's even here. It wasn't until he came across the community puzzle area and the disasterpiece of a puzzle a bunch of 7 year olds left it in when "trying to help" that it no longer became the community puzzle but the Derek puzzle because "the rest of you can't be trusted with it".

You can bet there is a passive-aggressive back and forth between Stiles and Derek through the Tip board, since Derek is elusive and hard for Stiles to get a hold of. When Stiles sees Derek's put a book on hold, he starts writing on the Hold Receipt (there were complaints about their squabble taking up the Tips board) before putting the book on the Holds for pick-up shelf.

"what kind of asshole takes over a community bonding activity for himself?"

Almost immediately after the book is checked out, Stiles realizes the gravity of what he's done. Oh shit, that's so unprofessional, what if he gets fired?!

However, the next day, a different book comes through the return slot with the same Hold Receipt for a HALE, D. On the back, under Stiles message, it says "they undid 3 days of work and forced the pieces together like a serial killer ransom note"

Phew, at least he doesn't sound mad. "Okay , sure, seeing your hard work destroyed by a bunch of kids sucks, but it's a chance for them to learn and be apart of something. You have grown up money. Be stingey at home!"

This goes on for a while. Everytime Stiles thinks he gets a clear picture of who Derek is, the guy will suddenly do something so unexpected and sweet, it makes Stiles rethink everything.

Like the time Derek donated enough food to the library food pantry to fill the shelves all summer.

Or the time the library was holding a friendly fundraiser competition between the kids and parents to see who would win a pizza party and Derek put 15 grand into the kids side.

Imagine Stiles' surprise when he finds out Derek is actually responsible for one of the library's biggest grants. They were able to open a whole Braille section because of him! Not only that, Derek's on the freakin board of trustees!

Derek practically owns most of the library and here he is letting Stiles berate him and call him names! What is he even doing here?! What kind of guy spends hours at the library everyday looking at nothing, talking to no one, and occasionally arguing with librarians about puzzles when he has money like this?!

It's not until one particularly slow day, when Stiles agrees to switch shifts with someone, that he finally gets to sit down and talk with the mysterious Derek.

Turns out money and time is literally the only thing Derek has left. His place is unbearably lonely, he never has to work another day in his life, and the library is the only place that ever really felt like home to him. It reminds him of his family and all the fun family and kids' programs they would participate in here. It used to be that, every morning, he didn't even know what he would do for the rest of the day when he woke up. It wasn't until he started putting his energy into the library that he started having a reason to even get out of bed. It started off small. Wanting to fix the puzzle. Then arguing with the librarian. Soon enough it ballooned into providing as much support and resources to the library and community as he could.

Stiles finds Derek to be very sweet and Derek loves how hard Stiles works to make everything fun and welcoming, especially for the kids. They talk, they go out for coffee, they joke, they laugh.

And, not for a lack of trying, they absolutely do NOT do a puzzle together for old times sake, because Derek is some kind of puzzle tyrant, and honestly it's kind of worrying.