When No One is Watching by Alyssa Cole

 This is a downright scary book. Sydney Green has moved back to Brooklyn after a bad breakup in Seattle. She's living in her mother's house, where she grew up, in a black neighborhood where a lot of the familiar faces are suddenly leaving and a lot of well-to-do white faces are suddenly appearing. At first she's just sad about losing her long-time neighbors, then she begins to wonder about what's really going on. The white guy next door, whose rich girlfriend has kicked him to the curb, becomes her partner (whom she doesn't totally trust) in trying to figure out what's happening. And what they find is shocking. 

Couldn't put it down--and it's quite a thought-provoking story.