Two factions, the Eco-Tech Coalition and the Revenants of the Prophet ("revs") are engaged in a futile war over territory and their competing social philosophies.
The ecologically-aware Coalition must hold back the zealous rev hordes constantly seeking new territory for their ever-expanding theocratic society.
Troids carry dozens of low-power paragliders, invisible to (otherwise) highly accurate energy-detection scanners, which dump several squads each of rev soldiers in the badlands beyond the borders of planoformed regions.
The difficulties begin when one of the revs he takes captive turns out to have been fashioned into a living bomb, a high explosive that Trystin evades only thanks to the jumped-up reflexes enabled by his neural implant, standard to all Coalition soldiers.
The conflict escalates further as the revs begin bringing in rocket launchers and stealth armor, making Trystin's job more and more trying.
He is forced to abandon East Red Three temporarily after one attack, and a final assault with hovertanks nearly causes him to lose a leg and the base itself.
He serves on board the Willis, under Major James Sasaki, a tactically brilliant man who is unfortunately deficient in piloting ability, and considered by many to have gotten his ship due to being from a powerful family in the arms industry.
Due to the fissioning of human society along roughly racial lines, much of the Coalition's population is somewhat dark-skinned and dark-haired, or very obviously of east-Asian stock.
Trystin comes from one of the rare few old-Anglo families in the Coalition, however, and his pale skin and light hair make him look just like a rev, who are predominantly Caucasian and fair-haired.
This makes "Brother Hyriss" popular to the women he meets on his way to Wystuh, for returnees are given special place in rev society for having been blessed enough to survive the brutal war, including permission to have up to six wives.
A large part of Modesitt's science fiction writing involves the construction of future societies, something not neglected in The Parafaith War.
While other societies, like the revs, look at the abundance of resources from controlling dozens of planets, the Coalition holds back from exploiting that bounty.
Caucasian people, such as the Desolls, are in a very small minority, but some family lines stretch all the way back to the founding of the Coalition.
While many Coalition characters are baffled as to how a religion based on an unknowable god gained such a foothold, it has had some benefits - social cohesion is high in the rev worlds, with almost no crime at all.
They are humanoid, with gray skin and hair, red eyes, greenish crystal-like teeth, and wide, flat noses that are really just an open slit in the face.
Their society is largely unknown, described as "an ultrahigh-tech, self-policing, consensus-based, anarchistic democracy based on environmental understandings and an overall technology that the Eco-Tech Coalition could only drool over from a distance."
The Book of Toren encourages the elimination of abominations, and so the revs are able to cloak their land-grab in terms of a holy battle between good and evil.
Corvettes and cruisers engage the escort of scout ships, which try to provide a screen against the Coalition's troid-buster nuclear torpedoes.
A single Coalition officer on duty can run nearly the whole station through his or her implant, needing only one tech on hand who has the expertise to fix what breaks down.
The revs are also employing near-perfect stealth equipment in their suits, making them nearly invisible to scanning and sight in most EM bands.
The Coalition does not have the numbers in both ships and soldiers to match the revs, and their technological advantage does not create a large enough gap to exploit effectively.
Translation of excessive mass increases chance of error, meaning goods cannot be ferried in massive amounts to border worlds.
Equipment occasionally burns out at perimeter stations and ship techs wait until the last minute to replace failing parts.
Rev corpses are even scrounged off the battlefields to be processed into fertilizer and organonutrient, necessary fuel for planet-side Coalition generators since fusion reactors ("fusactors") are forbidden in all but deep space.
For food, soldiers are often left consuming Sustain, a nutrient-energy drink made of water and powder mix; algae crackers; and other synthetic materials.
The Coalition economy is very carefully controlled, and Trystin has known the mass transit system of his homeworld to only ever cost two credits to get from the spaceport to home.
Later, on leave before his intelligence training, Trystin discovers his mother has died due to the strain of boosting her reflexes and metabolism through her own implant, while protecting a young relative during the first of numerous anti-rev riots on their world.
Politics has become a game of who expresses the most hatred for the Revenants, with nobody willing to take the blame for mismanaging the war or refusing to effectively deal with the problem early on.
Countless young men are sent off to fight the "Ecofreaks," and due to translation error on the troids they may not be seen again for 20 or more years, if they even survive their holy mission.
So many people support the war at all because they have bought completely into the belief that the Coalition is a danger, and that the Ecofreaks would come and eliminate them all or force them to take the abominable implants.