It starts in London with Mary Jekyll, mixes in mysteries (is Dr. Jekyll still alive?), suitably dismal nuns (caring for Mary's half-sister, Diana Hyde), adds in a bit of Holmes and Watson (on their way to another gruesome murder scene), further explores what Dr. Jekyll was trying to do (oh, and he was an alchemist, and they had this alchemist's society), and goes on from there.
It's not just one girl's quest for anything, though: there's the mystery of whether Mary & Diana's father is still alive. Mary tries to hire Sherlock Holmes for the task. There are other interesting people that they meet, especially the women. There is some science involved, and sexism (c'mon, it's the Victorians). A bunch of nuns trying to teach poor women some work skills to save them from sin, in suitably dreary conditions. And a couple of ghastly murders occur, too.
If this sounds anything like your cup of tea, READ THIS BOOK. Like Jae said: Theodora Goss is a fucking genius.