This is an interesting book. I read it in high school, and liked it, and decided to revisit it.
It's an intriguing blend of fantasy and sci-fi. And not in the science-fantasy way, like Star Wars, but in a real high fantasy meets hard sci fi way. Some delightfully archaic concepts of future tech, such as data stored on tapes, etc.
Rod Gallowglass is an undercover agent for SCENT, an organization that seeks to spread democracy across the galaxy. In this future, communications have improved to the point where pure democracy is possible, with every human having an equal say in all aspects of the government. This is presented as an ideal, though I strongly disagree, but that's beside the point. Gallowglass lands on a planet that split off from the main human culture centuries before, having deliberately cut itself off from technology to the point of total ignorance of their past history. They live in a bizarre faux medieval setting, with cultures and eras mixed as badly as a Ren Fest (I enjoy this particular point, because Ren Fests annoy this history nerd on a certain level for just that reason). He lands in the middle of a volatile political situation with three warring factions supporting absolute monarchy, warlordism, and totalitarian communism (though a weak straw man only) respectively. Gallowglass suspects off-world influence, given the sophistication of some of the political dogma (spoilers, duh, he's right). There is also a class of people who appear to have powerful telekinetic powers, known locally as witches (and warlocks, obviously). As the title suggest, they are rather important to the plot.
Written in 1969, this is a book that absolutely must be placed in context. It was written during Vietnam, and the Cold War in general, and the political allegory is very, very weakly disguised. Though it must be said that none of the three are shown to be purely evil, just flawed, with Gallowglass' democratic ideal as the true goal. A bit simple, but not unreasonable given the time period. There is also some slightly off-putting sexism from the main character. I think, THINK it's deliberate, as the character he targets is often far more capable than he, and he often finds himself reversing earlier statements. Still, I'm not entirely sure of the author's intent. It's a minor distraction, though. It's not great literature, but there are some intriguing sci-fi ideas in there, nicely cross-bred with fantasy.
Also, he has an epileptic robot horse.