The story alternates between past and present threads, weaving the timeframes together in such a way that each informs the other. In the beginning, we are introduced to Breq, a former soldier on a quest for revenge. She's come to an isolated, icy planet in search of the means for her revenge. Through the alternating timelines of each chapter, we learn that Breq used to be a segment in an artificial intelligence that ran a ship called Justice of Toren. There are layers of hierarchy and organization, but basically these ships are comprised of networked groups of Ancillaries, dead human bodies with the AI embedded into them. This is not a conceit or an idea for the sake of ideas; the exploration of this sorta post-human existence is the primary driving force behind the book. In Breq, a single body separated from her whole, we get a unique perspective on this sort of existence.
For her part, Leckie is able to establish all of this without resorting to excessive info-dumps. This is initially disorienting (though not as much as, say, The Quantum Thief), as the thread set in the past sometimes reads like a Pynchon novel, with the one AI's perspective shifting from Ancillary to Ancillary with each new sentence. It's disorienting because they're the same person, but they're thousands or even millions of miles away from each other, but once you get the hang of it, it works (in particular, the naming conventions of the various levels of hierarchy can be confusing at first). Interestingly, the more info-dumpy segments come later in the book, but by that point, you're wrapped up in the story enough that this information is happily received.
So the way the AI ships work is one aspect of the worldbuilding that works very well, but the other aspect is the social one. Being a space opera, we're of course talking about galactic empires and wars and such, but the empire that Leckie has established here is truly a fascinating one. The Radch are the dominant human society in the galaxy, having steadily annexed planet after planet over a 2000 year period. Of course, annexation in this context is a just a pretty word for conquered. The humans on an annexed planet that resist are killed and turned into ancillaries, which are then turned against the people. Comprehensive surveillance at the hands of Ancillaries makes it difficult to resist, but that's just the Radchaai way. Even the soldiers who are doing the annexing, the Radch citizens, do not receive any privacy. This goes on until a planet is pacified, and the Radch sink their hooks into the planets economy, leveraging gains (in both wealth and ancillaries) to annex other worlds. So basically, the Radch are not very pleasant folks. The Radchaii are lead by someone named Anaander Mianaai, who is very much like the artificial consciousness that run Radch ships in that she is comprised of many networked bodies. She's also near immortal and has basically been the Radchaai dictator for 2000 years.
The Radch identify each other mostly through Houses, tribal affiliations that are complicated and corporation-like. One corollary to this is that the Radch do not distinguish between genders, referring to everyone using only female pronouns like "she" and "her" (it is not explained why the female form is chosen over gender neutral ones, like some other authors have used). Breq, our protagonist, is implied to have a female body, but being an artificial intelligence of the Radch, she makes no distinction between male and female for herself or for others. Breq constantly has difficulties identifying gender when she is outside of the Radch empire (as she is in the present-day segments of the story). This aspect of the novel has garnered much praise for its progressive tendencies, though I'm not entirely sure the book means it to be read as a good thing. It certainly does generate some interesting discussion for us readers, but in the context of the book, it's a conceit imposed by a tyrant. Anaander Mianaai is many things, but one thing she will be to the reader is "evil". And the reason for this gender-blindness is simply her will. Just as it's her will to impose comprehensive surveillance on all citizens, or as we discover in the book, to slaughter innocent citizens by the thousands. And this is supposed to be progressive?
It's an interesting perspective, for sure, and while the constant use of female pronouns is initially jarring, it quickly fades away, partially because you get used to it, and partially because the Radch simply don't care and this story doesn't really need it (though it's implied that reproduction happens in a generally traditional manner, with perhaps some SF technological help (which, in itself, implies that the distinction must be made at some point, simply for reproductive purposes)). Still, the more important social structures seem to be the Houses and how they interact. Put simply, there's lots to chew on, and Leckie does seem to be aware of what came before her, as io9 notes:
For people who love science fiction, there are also many little tips of the hat that are pleasing without being intrusive or fan servicey. Breq's division on Justice of Toren are fond of singing, which brings to mind Anne McCaffery's incredible novel of ship consciousness, The Ship Who Sang. And of course the Radch civilization's lack of gender roles is reminiscent of the civilization that Ursula Le Guin describes in The Left Hand of Darkness. But as I was reading, the one comparison I kept making in my mind was to Iain M. Banks, who always reminded us that politics (and people) are far more complicated than most space operas will allow.Incidentally, I'd say this novel blows The Ship Who Sang away when it comes to exploring ship consciousness, but on the other hand, I found Le Guin's novel much more mind-blowing in terms of its gender bending (but then, that's a tough act to follow and not really a fair comparison for this book). And as mentioned recently, I really do need to get up to speed on Ian M. Banks.
So yes, this book has an impressive bit of worldbuilding going on, but it's all revealed slowly through the story, which has plenty of narrative hooks to keep you interested. Mystery, action, typical space opera tropes, an alien race that seems to be truly Alien (capital A, though we've not learned much about them just yet), that ambitious exploration of hive minds, and other ideas that help build and maintain the sensawunda feeling that comes out in the best SF. I really enjoyed the novel, and it's something I'd consider nominating for a Hugo award, if I end up submitting a ballot. As debut novels go, this is an assured effort, and I'm greatly looking forward to the next installment (due in October 2014).