In Enemy Territory by Shannon West

What should a Tygerian colonel do when he develops a devastating and disastrous attraction that’s totally unsuitable?

Kylon Bonnett, close friend of Prince Mikos, goes to the aid of Prince Larz on Laltana when both they and the disgraced human prisoner, Rasc Centarlo become embroiled in a mission to the unfriendly prison planet of Gatifrey. A deranged commandant there is harboring a deadly secret, and playing a dangerous game with the prisoners’ lives.

Prince Mikos and Ryan’s paths converge with Bonnett’s and Centarlo’s in a surprising way. They discover the commandant’s true identity and find themselves in grave danger, when it becomes a contest between them and the commandant to see if they can survive this mission that takes them deep into enemy territory.