For a medium as limitless as science fiction, truly new and unique ideas can be hard to come by; that's one of the things that makes this book such a treat. It is a space opera full of political intrigue and moral ambiguity from a truly unique perspective - Breq, the AI of a spaceship, once spread among many reanimated human hosts - the titular ancillaries - now reduced to a single body, for reasons revealed over the course of the book. Sidestepping the trope of the emotionless computer, AI in this world are designed to feel, to facilitate their decision making, but there is still an alien quality to Breq's experience, expressed with lovely, inventive language. This is hard sci-fi - there's an emphasis on technological details, solid world-building, and internal consistency, but it doesn't suffer from the static prose that sometimes plagues the genre, making it an accessible, yet engaging, choice. I cannot recommend this title highly enough.
Now isolated in a single frail human body, Breq, an artificial intelligence that used to control of a massive starship and its crew of soldiers, tries to adjust to her new humanity while seeking vengeance and answers to her questions.