This book kind of blew my mind (and brought back my rabid Iain Banks fandom, after the slight disappointment that was Excession). It took me a long time to read, partly because it's 600 pages long and partly because the hardback copy I have is too heavy to want to take on vacation, but also because it's thematically so huge that I kind of needed 4 months to digest it.

There are, of course, several interleaved plots, but the overarching one (introduced early enough for this not to be a spoiler) is a conflict about whether Hells should exist. This being the universe of the Culture, this is not a metaphysical question, but a purely ethical one, because civilisations can choose to have a hell or not, and that choice has become a major division between and within civilisations.

As I read the book, and plenty happened in my own life and the world in that time, what made me really love it was the number of parallels I saw between its techno-fantasy world and the real world around me. The sadism embodied in the Hells, the repugnant status-quo-at-all-costs reasoning used by those who would justify them, the sometimes hopeless-looking idealism of those who would get rid of them, and the weaknesses and limitations of all the would-be good actors all felt like biting commentary on events this year that Banks couldn't have exactly foreseen. And then there's the moral ambiguities of just what steps may or may not be justifiable in service of a noble goal (not exactly a new theme for the Culture novels, or the best exploration of it I've seen, but certainly an engaging one), and the multiple levels of different actors manipulating each other. Of all the Culture novels, even as it has one of the more outlandish plots, I think it's the one that has most to say about the world we actually live in.

NB: If you haven't read any of the Culture books before, don't start with this one because it definitely seems to assume you know something of its world.