Ancillary Justice by Ann Leckie is set thousands of years into the future when the Radch Empire is the primary galactic power of human-occupied planets and security is maintained by AI-led spaceships with AI-controlled human soldiers (ancillaries).
The main character, Breq, appears to be a soldier seeking revenge, but in reality, she is the last remnants of an AI mind in charge of the starship, Justice of Toren. With only partial recall of her circumstances, Breq pieces together the events that led to her fall, before undertaking a bold quest to kill the all-powerful Lord of Radch Empire, an AI ruler inhabiting multiple bodies.
The plot switches between two timelines. Breq's present-day quest for justice after her ship's destruction, and flashback to the past events leading to her fall.
This deserved winner of all the major SFF awards in 2014 showcased Leckie's writing skills. She is just as assured in her intricate character study of Breq and her reluctant companion Seivarden, as she is with her sweeping space-operatic world build. If not for the demanding and sometimes confusing first section, I'd give it a top rating. 4.5 STARS