Frostfire (Kanin Chronicles, Bk 1)

Bryn Aven is an outcast among the Kanin, the most powerful of the troll tribes. Set apart by her heritage and her past, Bryn is a tracker who's determined to become a respected part of her world. She has just one goal: become a member of the elite King’s Guard to protect the royal family. She's not going to let anything stand in her way, not even a forbidden romance with her boss Ridley Dresden. But all her plans for the future are put on hold when Konstantin– a fallen hero she once loved – begins kidnapping changelings. Bryn is sent in to help stop him, but will she lose her heart in the process?