Didn’t See That Coming by knittersrevolt
Slash Derek/Stiles
http://archiveofourown.org/works/1185521?view_adult=true&view_full_work=true

Great story that is just hilarious in parts. In this case all of the characters are older, late 20's mid 30's and the Hale family is alive. Stiles husband Scott cheats on him and Stiles decides to leave Beacon Hill for New York. There he runs in to Laura Hale, ends up the adoptive (sort of) father of a baby werewolf and Derek's mate. Soon he learns magic and exorcism and unfortunately must return to Beacon Hill. The characters are well written and being older gives them a new dimension. The author has really pinned down Stiles attitude and his use of protecting sarcasm. Peter is still a creep, Scott is still in denial, the sheriff just wants his son back and Derek still is too sexy for a small town. With an older cast you have different sorts of problems, children, jobs, businesses, etc.... I love Stiles one liners and the baby Samantha is too adorable.
Excerpt:

To Derek: It’s not too late. Elope with me. Vegas is only 11 hours away.
From Derek: Gay marriage is still illegal in Nevada.
To Derek: Really? That’s bullshit! If I want to make bad impulsive life choices while on a high from gambling I should be able to!
From Derek: Your Dad is giving me the stink eye for texting. Just get down here.