Star Axe. Rim Chronicles Book 8, #8

An occupied world. A slave labor mining camp. Two captured Fleet officers. And a frontier god who could no longer stand to watch innocent lives perish. The conflict between the Shoultain Warlords and the Federation has been going on for millennia but only through a series of skirmishes in the Neutral Zone. The latest such conflict, precipitated by traitors within the Fleet ranks, results in the capture of two young Fleet officers, Chief Medical Officer of the UGS Trevor Meridian, Karin Vexley and the ship's second rotation navigator, Kitaya DeWynter.
Their ship can't assist them in any way, because that would constitute an outright declaration of war. Their friends and loved ones can only look on from outside the Neutral Zone, helpless in their anger and grief. All the prisoners captured in the latest engagement are brought to Yerendor, one of the six worlds that fifteen years ago, the Federation surrendered to the enemy in exchange for signing a peace treaty.
All six worlds have been turned into fearful slave labor camps. Karin and Kitaya's chances of surviving the brutal internment would be slim if not for one of the frontier gods who defies her membership to come and help the child she raised as her own. The same engagement that resulted in Karin and Kitaya's capture, saw Captain DeWynter carry out his questionable mission with success. But like most things in life, that success came at a very high price that may not see him remain in the Fleet for much longer.