If you haven't read The Wall and the Wing (and if not, why not?), then I must say that I really think it best if you go off and do that before you pick up The Chaos King, even though a brief plot summary is provided in the early part of the book. It will help you to understand the alternate world much, much better than you'll be able to if you just read the second book, where some things (like why everyone's so eager to get to the Hall of Flight at the museum, and who the Professor really is, and the true nature of cats) aren't really discussed in enough detail to make sense. They're mentioned, and I doubt you'd be lost, but you might not understand the import/backstory as well. And besides, The Wall and the Wing was a truly terrific fantasy -- and an original concept. No elves, fairy/faerie, mystical languages/quests or any of the other stuff that smacks of British fantasy -- it relies on sheer American ingenuity and the quest for invention.
Ah, but I meant to be talking about the book. Right.
The Chaos King, like its predecessor, begins with a prologue, cleverly titled "The Chapter Before the First". Also like its predecessor, the prologue focuses on the Professor, a man fond of wearing women's housecoats, with grass instead of hair, pocketsful of kittens, and an "answer hand" that he bought from a guy on eBay. Only instead of hiding in his home/lab (like usual), we find the Professor on the run from a new character named Mr. Fuss. We know Mr. Fuss wants to take something that belongs to the Professor, and that he's working for someone else. And we know that the Professor is afraid. Afraid enough to allow himself to be swept out to sea, rather than let Mr. Fuss get his hands on the device.
Cut to the first chapter, where we catch up with Georgie, known in most of the first book as "Gurl." Life as the Richest Girl in the World isn't particularly fun, we learn, largely due to Roma Radisson (Paris Hilton very thinly disguised, no?), the Second Richest Girl in the World, who resents pretty much everything about Georgie. And hey, Georgie resents parts of herself at this point -- she's had a growth spurt, she's promised her parents that she won't use her power of invisibility (yeah, you read that right), and she's had a falling out -- or at least a falling off -- with Bug (Sylvester Grabowski, son of an infamous mobster), her only friend from the time before she was reunited with her parents, now a major athlete and advertising icon.
As it turns out, Mr. Fuss knows that Georgie and Bug were friends with the Professor, and he thinks they may have what he wants, so he goes against his boss's orders and decides to meddle with those kids after all, using a Punk who has renounced the name Sid, and instead uses the handle "Mandelbrot," as in the mathematician associated with chaos theory, not as in the almond biscotti of the same name. Mandelbrot is the Chaos King, complete with odd personal habits like spontaneous dancing, lapses into pig latin, and a preference for making art out using food products. And, oh yeah, the vampires like him because he's interesting to watch.
And in (alt) NYC, there's a decent amount of chaos afoot. Bug is dragged off a pier into the river by an enormous octopus soon after a fossilized giant octopus disappears from a museum. Gurl sees an abstract statue come to life and "bite" Roma at the art museum. And then Bug meets up with a giant sloth while filming a commercial. And I'm talking King Kong-sized giant sloth, here, complete with an Empire State Building climb while holding a pretty blonde. Is The Chaos King behind it?
This book features mystery, intrigue, and clever kids. Vampires, crows, talking birds, web-surfing cats, a rogue poet, and one very powerful librarian. More than that, I will not say, except that if you're a fantasy fan, you should seek this one out. After you've read The Wall and the Wing, of course.