This sprawling science fiction book by Anne Leckie was initially quite a challenge to engage with, but ultimately very satisfying. I persisted because this was my book group's selection and because this book took several of the top sci fi awards (Hugo, Nebula, and Arthur C Clarke among others). The protagonist is a remnant of a huge military warship's AI system who has managed to figure out that the supreme ruler of the Radchaii (who essentially rule the civilized human universe) has developed a split personality and that one part needs to be stopped, i.e., killed. Our protagonist (variously known as Breq, One Esk, or Justice of Toren) escaped the destruction of her ship by that same ruler and, in the body of one augmented human, is on a quest to find a weapon of alien origin that could be used to avenge the murder of her favorite ship's officer, her ship's captain and crew, as well as the destruction of her ship, Justice of Toren. It is such a detailed storyline and set across such an enormous span of time and space, that it is hard to summarize. Suffice to say that if you can stick with it for the first 150 pages, you will get hooked.
There's a very good review of the book at NPR