The book takes place on a fictional planet based on late-Middle Ages Europe. It alternates chapter-by-chapter between two concurrent storylines. One storyline follows Vosill, a king's personal doctor, told from the point of view of her apprentice. The other follows DeWar, the bodyguard of the military dictator of a nearby country.
At one point DeWar tells of a pair of close friends who disagree about how an advanced society should manage contact with more primitive cultures:“ Was it better to leave them alone or was it better to try and make life better for them? Even if you decided it was the right thing to do to make life better for them, which way did you do this? Did you say, Come and join us and be like us? Did you say, Give up all your own ways of doing things, the gods that you worship, the beliefs you hold most dear, the traditions that make you who you are? Or do you say, We have decided you should stay roughly as you are and we will treat you like children and give you toys that might make your life better? ”
—Inversions, chapter 6
It is evident that Vosill and DeWar are these two alien friends, now no longer in contact with each other, who have both come to the medieval planet and are independently attempting to do the "right thing" in their own differing ways, with Vosill attempting direct intervention and DeWar being more passive.
The book stands out in the context of the Culture novels for the relatively confined space in which it is set - the other novels tend to span many worlds, and often much longer timespans. Inversions represents the most intimate portrayal in the Culture series of the ways in which Culture citizens can affect the paths of other societies.