Warning: Wikipedia contains spoilers.
Banks has written a series of novels set in a single universe which are referred to as Culture novels, and the status of Inversions in this respect is arguable. Unlike the other two most recent novels in the series, Excession and Look To Windward, it is not declared a Culture novel on the cover. It is made quite obvious to readers of the other Culture novels, however, that the two protagonists hail from the Culture, a vast and extremely advanced society with a predilection for interfering in the development of less sophisticated societies. It is interesting to note that in the initial hardback printing of the book, the word "culture" has a capital C when it appears in the prologue. In the mass market paperback printing of the book, the C is lower-case.
Like many other Banks books, Inversions has a nested structure; we are introduced to the tales by the grandson of the purported reporter of one of them, thus giving us three or four distinct layers of supposed narration (the two original fictional "authors", the fictional "editor" and Banks himself). Through these layers the story we are told is fundamentally about states, how they are built, how they interact and how they change - and how individuals can change them. The two interlopers were intimate friends in the Culture, before each came to intervene in the affairs of this world; they develop different notions of the extent to which change can morally be enforced on an unwitting weaker society, and the two outlooks seem to be reflected in the way they choose to intervene in the societies they come to influence.
The book is unusual in the context of the other Culture novels for the relatively confined space in which it plays out - the other novels tend to span many worlds, and often much longer timespans. It represents the most intimate and microscopic portrayal in the Culture series of the ways in which Culture citizens can affect the paths of other societies.