This is book three in the Elemental series by Brigid Kemmerer. Unfortunately, it's been long enough since I read the first two that I really had no idea what had happened going into this book. It was still great, but I definitely recommend reading them closer together instead of years apart. :P
I'm also going to issue a spoiler warning for the first two books because I don't remember what was revealed and what was already known through those.
This book follows Hunter, a "guide" - someone who can sense other elementals, but who is encouraged to eliminate them. The elementals he is familiar with are all other teenagers in his hometown who can each control one element; air, earth, water, or fire. He struggles to balance everything going on with his life. His mother and grandfather mistreat him, especially since other students are framing him for crimes he did not commit. He works to reconcile what he knows about the other elementals with what he's always been told about them - that they're dangerous. He's also intrigued by a new girl in town who seems to have something to hide.
I liked this book, if only because it diverged from my recent streak of romance novels. Although it did have a romance plot line, it focused more on the paranormal aspects of Hunter's life. It gets a four out of five, because it was pretty fantastic.