Book 1 of his Midnighters series. I got this out of the library after hearing Westerfeld say interesting things on an episode of the Tor Podcast. (Just in case anyone at Tor is wondering if those things lead people to their books. In this case, at least, yes.)
Jessica Day is a teenager who has moved with her family from Chicago to the small town of Bixby, Oklahoma. Shortly after starting school she discovers that something strange happens to the world every night in Bixby but she and a few other kids in the town are the only ones who can perceive it.
One of the things I liked about it is that the strangeness has been going on for a long time prior to the arrival of the protagonist. While this is a handy storytelling device, allowing lots of plausible info-dumps, it also nicely defuses most of the aura of “chosen one” about Jessica since she has peers who have spent years working to make sense of their world.
The book is a quick read and the setting is intriguing enough I may pick up the next couple books.