Canyons of Night: Book Three of the Looking Glass Trilogy by Jayne Castle

The island of Rainshadow is home to the mysterious, privately-owned woods known only as the Preserve. Now, after fifteen years away, both Charlotte Enright and her teen crush, Slade Attridge, have returned. But will their psi talents and Slade's dust bunny companion be enough to keep them from getting drawn into the darkness at the heart of the Preserve?