I'm on a role with these series. :)
The Beka Cooper trilogy, by Tamora Pierce, is one of her Tortall books, taking place in the same world as her Lioness Quartet and her Wild Magic Quartet, which offers a bit of a peek into the world and the way it works for common folk that don't hang out with royalty.
Have I ever mentioned how much I LOVE worldbuilding?
I'm not going to summarize the series - that's what reading is for, and it's also the entire point of picking up a book. I will say, however that this series is something unique that I don't think I've seen much of in the world of literature, though it does show up sometimes in television series.
Beka Cooper is what I might call a "spinoff series," or maybe a "supplementary series," adding to the worldbuilding of the "main" stories that take place in this world. It's not the only one, either. The Protector of the Small series serves a similar function, though it shows some of the "main" characters from a slightly different angle.
What I'm trying to get at here is that after establishing the world in the original work, she didn't just let it sit. The author went back and fleshed it out, explored the implications of certain rules, and asked a series of really interesting "what if" questions that resulted in more books, which I adore.
For the series as a whole, I'm dropping five gold stars right here. I love not only the fact that this is a worldbuilding extravaganza, but also a story that takes a new angle. Most of the characters in the Tortall books are nobles, going through hard times and trying not to lose face, but not in danger of losing homes or going without food (in general). This series focuses on a girl from the gutter that stays in the gutter, more or less. She doesn't become a knight or noble, she doesn't marry the prince or move into the palace. She's a girl from the lower city that grows up wanting to help people in the lower city and gets a job working in the lower city.
AND I LOVE IT.
Fantasy work ethic. It makes me happy.