Blue Noon by Scott Westerfeld is the third and final book in the Midnighters series. You can read reviews for the first two books here:
I was so pleased with the completion of this series. Rex, Melissa, Dess, Jessica and Jonathan are surprised during the pep rally when the entire gym turns blue and the Midnight Time encroaches on real time. Melissa can taste the darklings celebrating in the distance because they have found a way to invade the human realm. After narrowly escaping becoming a halfling, Rex is surprised at his new-found abilities. Can he and the others prevent the darklings from turning Bixby, Oklahoma into a twenty-five hour a day feeding ground?
I loved the ending of this book and I found a few good quotes along the way as well:
If you have ever felt like you were an outcast and didn’t quite fit in with the rest of the world, join the world of the Midnighters.