I took a chance, because it was a fixit and I was jonesing -- and I ignored the whole "original character" thing and I dove in and ...
Oh my god, guys, seriously. You will love this fic. You will love everything about this fic. It doesn't matter if you like Sherlock or not, or if you like OCs or not. But if you do like those things then you'll be overjoyed. And if you don't it won't matter because it is a truly wonderful, in-character Fixit, and Donna and the Doctor are gorgeous in it.
Read it. Read it now.
"Recovery" by PlaidAdder (on Ao3)