That's the one I was reading in Taiwan, that I said you would probably like but you had to read the previous ones first. The Guards books deal a lot with race relations and prejudice, as the Guards (police) deal with a more pluralistic society, and must themselves (sometimes forcibly) accept members of races, species, genders, etc which they've never had to before. Feet of Clay, an earlier Guards book, is about the exploitation of a particular group of beings, and involves Jewish mythology.

And they're very funny! And sometimes spooky, poetic, and magical.