The Fallen Moon, book 1: The dark griffin
Katie J. Taylor2010

In the land of Cymria, humans and griffins rule side by side ... Arren Cardockson is a despised Northener, a people conquered and enslaved centuries ago. By freak chance, he became a griffiner -- chosen by a griffin as their companion -- but many resent and fear his existence. Meanwhile, chained in a cage behind the fighting Arena where rogue griffins entertain the crowds, the mysterious black griffin dreams of escape. Arren's meeting with this renegade griffin sets his life on an inexorable path of murder, conflict ... and an encounter with his past. DARKNESS CANNOT BE CAGED.