"That bitch knew everything. She had been in on it from the start."
This novel starts off as a fairly Dickensian historical piece. Set in 19th century London among a loose knit family of thieves with the requisite odd names to go with it. The man of the house is a Mr Ibbs, who spends much of his time melting gold off of coins, just a little so as to not lose the value of the coin, but enough to acquire a bit of gold . The lady of the house Mrs. Sucksby, runs a quasi adoption agency, taking in babies of local prostitutes and other shamed girls, and then selling the babies for a profit (after keeping them quiet in their cribs with nips of rum). One of the few older girls there is Sue Tinder (names does mean something), who has always received better attention from Mrs Sucksby. Sue does occasionally participate in some of the less noble activities there -she learns how to make keys for one, but in general is kept out of things. This changes with the arrival of Gentleman, a family acquaintance who has an idea for a wonderful swindle that requires Sue to join in.
I'm loathe to give much of the plot here, other than to say it is incredibly complex and has a tendency to fold back on itself multiple times. Its not too much to say that this is a mystery, and a lesbian romance (I think pretty much every Sarah Waters' book is). There is a weird old guy who is cataloging literary porn because....someone has to do it(?), a girl, Maud Lilly, who has been raised incredibly cloistered except for one small, nah, huge, exception, and a lot of skullduggery concerning who exactly people are. And an insane asylum, and a knife, a playing card...
One of the great things about this book is the way it does the unexpected - in some novels this comes at the expense of misleading the reader - but that's not the case here - you are put in the same seat, with the same knowledge as some of the characters, and things aren't always what they seem to them. Vertigo essentially employed this same process, and that turned out well. In Fingersmith, this is even added to by not having everything revealed at once. We think we are done with the surprises, but more keep coming. There is a labyrinthine scheme going on here that is not the one you think, even a few pages from the end. And characters who can be exceedingly good while at the same time exceedingly bad.
I suppose, too, this is about family. While we don't have families in the traditional sense here - the two main characters have never known either of their parents or immediate family members, and there isn't a single normal parent-child relationship in the book, the allegiances, and responsibilities, are the same and play an important role in what goes on. More importantly, we get to see what happens when the foundations of families prove to be in one way an illusion, but remain steadfast in other ways.