Bound By Fire. Rogues of Magic Series, #3

Ancient dark magic has taken everything from Ann, but she has the one thing Urien doesn't. Hope. Edward Rohn is not only Ann's guardian, but her best friend. While his feelings for her begin to grow into something more, Ann helps him unlock memories of his familial ties to the lycans of Lulrien, as well as his destiny. He's meant to guide the wyverns and lycans into an era of peace, just as he's meant to protect and guide Ann, the archdruid who has captured a piece of his heart.
Ann's half-brother, Urien wants nothing more than for Ann and Ed to fall into a false sense of security. While he infiltrates Lulrien with spies, he works on his latest scheme. He's uncovered the key to the underworld where he can unleash an army powerful enough to take Ann's power. and her life. All he needs is to find its door in the bowels of Lulrien and unlock it.