So, I couldn't help but superficially compare things in this story to Pitch Black and the Chronicles of Riddick. On a surface level, the Doctrine (of which Sergei is a captain) is rather like the Necromongers, spreading their Doctrine across the universe a planet at a time with their "we are one" collective philosophy. (They all call each other brothers.) They reach the planet Cirokko (a combination of the terrain and natives of the planet from Pitch Black with the hot/cold nature of Crematorium on a seasonal basis), and they receive resistance from the planet's natives. Not the first time. Cirokko is called the "Fool's Gambit". 
 A new general and new aide-de-camp start a new campaign planetside. Only now a rebellious faction called the Alliance has inserted itselves amongst the natives (some of which are lizard-like flying creatures) and seek to stop the Doctrine regime from taking the planet. Enter Mike, a sergeant with Alliance CovOps, who sees a weakness in Sergei he can take advantage of to get closer to the Doctrine command and find out their plans, then feed them to other CovOps members running with the resistance in the mountains. 
 Only Mike's plan works too well and he falls for Sergei as Sergei falls for him (against his inDoctrination, which is part of why the Alliance calls all of the Doctrine soldiers zombies). Now he doesn't want Sergei to get hurt when he and a batallion are suddenly deployed into the mountains, exactly where the last batallion was obliterated by the natives. And that's only the first half of the story. 
 Really, the similarities really are only superficial, but it entertained me to compare between universes as I was reading. Mike is sympathetic to the reader in that he knows he is breaking Sergei's trust and that Sergei deserves better than he (or the Doctrine) has given him. He sees how Sergei is being repressed because he doesn't know any better. He sees how free Sergei can become of his inDoctrination, and it tears him apart to know in the end his betrayal will destroy what they have shared. 
 Sergei doesn't know anything but the way of life imposed by the Doctrine. He knows he is flawed by Doctrine standards and worries that he will bring shame to his family by being unable to properly follow their standards. He worries that he brought his batallion to ruin, all their lives lost for nothing because his general sought to get rid of him and their lives became forfeit in the process. He worries they'll wipe his mind and he won't remember what little happiness he shared with Mike. He worries Mike will die in the hostilities (before he finds out who Mike really is). 
 It's a well-woven story of two soldiers from opposite sides who find love without meaning to. Neither figures they have a real chance for happiness because their beliefs are too far apart to come together in the middle, too much betrayal and hurt to get back to the hope they shared in each other. But there was always love.