Alliance-Union Universe: Hunter of worlds by C. J. Cherryh

The iduve were the most advanced spacefaring race in the galaxy. They travelled where they pleased in giant city-sized vessels, engrossed with their own affairs. The iduve were humanoids–with a difference: they were predators incapable of human emotions.
Aiela was a world-survey officer who found himself abducted to serve the iduve clanship Ashanome. Forcibly mind-linked with two other humans, life became for him wholly intended for dedication to the service of his captors.

But events involving a human world that had become prey to the Ashanome were to bring out contradictions and confrontations that make the story of this man and his captor-master, the Hunter of Worlds, a truly powerful science fiction novel.