Beautiful Darkness - Kami Garcia

Ethan Wate used to think of Gatlin, the small Southern town he had always called home, as a place where nothing ever changed. Then he met mysterious newcomer Lena Duchannes, who revealed a secret world that had been hidden in plain sight all along. A Gatlin that harbored ancient secrets beneath its moss-covered oaks and cracked sidewalks. A Gatlin where a curse has marked Lena's family of powerful supernaturals for generations. A Gatlin where impossible, magical, life-altering events happen.

Sometimes life-ending.

Together they can face anything Gatlin throws at them, but after suffering a tragic loss, Lena starts to pull away, keeping secrets that test their relationship. And now that Ethan's eyes have been opened to the darker side of Gatlin, there's no going back. Haunted by strange visions only he seems to see, Ethan is pulled deeper into his town's tangled history and finds himself caught up in the dangerous network of underground passageways endlessly crisscrossing the South, where nothing is as it seems.