Unbound Instinct (Star Tracers, #2.5)

Vex was born into servitude, collared and trained into submission by the Xen'dari Empire. An unexpected turn of events offers him the chance for freedom, but Trexen were taught to fear it, and themselves. Without the Xen'dari collar around his neck, or a Master to tell him what to do and how to do it, Vex is faced with having to make his own choices while fighting against the instinctual, carnal nature of his Trexen heritage. Cris is the last of her kind, enslaved by a man who uses her char...