In it, Susan Trinder, a "girl from the wrong side of the tracks" (Borough in London), teams up with a "well to do friend" of her "aunts," to separate a naive heiress from her money. Along the way there's cross and double-cross as the two heroines (you'll be rooting for both by the end), the "well to do friend" and the "aunt" all vie for the cash.
The story night seem clever, but I wasn't convinced. Maybe it's because I'm a man (many of the positive review are from women). Maybe it's because I've read a lot of crime fiction (and so could guess the story), but I didn't buy into the premiss of this book, or the "double cross" on which it turns (I could see it coming from the moment the "set up" was introduced).
So in short I was underwhelmed by the crux of the story. It's well written. The descriptions of Victorian London were interesting. The core story, however, dragged. Couple this with the fact that one of the heroines wasn't particularly pleasant during the important second third of the book, and the book was lessened for me.