The White Gryphon (The Mage Wars: Book 2) by Mercedes Lackey and Larry Dixon

It has been 10 years since the magical Cataclysm which destroyed the twin strongholds of the two world's most powerful Mages, killing Urtho, creator of the gryphons, and sending his forces into exile. Now Urthro's peoples - human and non-human alike - live in a terraced city carved into the face of a gleaming white cliff on the edge of the Western Ocean. Secure...at least until the fleet of the mysterious Black Kings appears in their harbor, bringing envoys who inform the residents of White Gryphon that their newfound home lies on the northern perimeter of lands claimed by this powerful kingdom. Desperate not to lose their hard-won home, Skandranon, along with his longtime friend Amberdrake agree to accompany the envoys back to the Court of the Black Kings, hoping to negotiate an alliance.

When a high ranking noble who opposes this alliance is found murdered, Skandranon and Amberdrake realize that they are up against unknown enemies who will stop at nothing, even the use of diabolical Blood Magic, to destroy White Gryphon.