The secret hour - Scott Westerfeld

Strange things happen at midnight in the town of Bixby, Oklahoma. Time freezes. Nobody moves. For one secret hour each night, the town belongs to the dark creatures that haunt the shadows. Only a small group of people know about the secret hour - only they are free to move about the midnight time.

These people call themselves Midnighters. Each one has a different power that is strongest at midnight: Seer, Mindcaster, Acrobat, Polymath. For years the Midnighters and the dark creatures have shared the secret hour, uneasily avoiding one another. All that changes when the new girl with an unmistakable midnight aura appears at Bixby High School.

Jessica Day is not an outsider like the other Midnighters. She acts perfectly normal in every way. But it soon becomes clear that the dark creatures sense a hidden power in Jessica . . . and they're determined to stop her before she can use it.