I just finished Un Lun Dun, which strikes me as The Phantom Tollbooth meets London Below. This isn’t a negative — I enjoyed both those books.
The book follows the Shwazzy (choisi), Zanna, and her friend, Deeba, as they go into unLondon, an abcity for London. (Other ones include Parisn’t, Lost Angeles, Baghdon’t.) The Shwazzy is prophecied to save the city from the Smog, which is like smog, except sentient. Lots of things are sentient here — Deeba picks up a pet, Curdle, a discarded milk carton, there are a set of guards called Binjas, trash bins that know martial arts, and so on. Lots of other things could be sentient, but have been somehow taken over, so there are a number of kinds of zombies.
Every now and then the overt political themes (not just “pollution is bad”, though it does sort of imply that air pollution is bad, but leaving garbage on the street is ok, because it will end up living in an abcity) show up a little too obviously, though I’m not sure children would catch it.
I love the sense of wordplay, in locations and names, especially when it’s not attached to the doom-and-gloom Bas-Lag books. (I like those books, too, but they’re depressing.) I loved, also, the subverting of a lot of fantasy tropes, most of which will be understandable even to children. (Some are, I think, a bit more subtle.)
It’s light, it’s funny — I have trouble saying that about a China Mieville book because hey look over there, hell has frozen over. But it is. It’s a long book, and the beginning needs some tightening up, and if you’re a big fan of giraffes, it’s not the book for you, but otherwise, it’s an excellent young adult fantasy.