Canyons of Night by Jayne Castle (Jayne Ann Krentz) Book

This is book three of the Looking Glass Trilogy. There are as many mysteries aboveground on the world of Harmony as there are underground. The island of Rainshadow is the setting for one of the greatest of those secrets: the privately owned woods known only as the Preserve… Growing up on Rainshadow, Charlotte Enright knew better than to ever go into the Preserve, until that one fateful night with Slade Attridge — a night neither of them would forget.