As the conclusion of the Radch trilogy, Ancillary Mercy closes out Ann Leckie great work of fiction with a fitting ending. Breq has established her connections throughout Athoek station in the previous book so this one concerns itself with the arrival of her nemesis, a portion of the Lord of Radchaii who has strong feelings of ill-will towards the narrator and the trilogy's Artificial Intelligence protagonist.
Justice of Toren is the rogue ancillary who has spent enough time asserting her authority as Fleet Captain to plant the seeds of a revolution. There is plenty of diplomacy mixed in with some complex action sequences. The appeal of the Radch trilogy is the heavy world-building and the way that world plays out. Traveling through space is not some immediate jump, though gates do allow for immeasurable distances to be crossed, but even during high tension, everyone must wait for a ship to make the journey.
I would highly recommend this book to fans of science fiction, especially those fans who enjoy worlds that have deep backgrounds that extend out into the universe. There may be some spoilers as I go along so I would recommend readers that care to stay away from the following two paragraphs, though it may be hard to understand what is going on. The book doesn't follow through on journeying anywhere outside of Athoek station and most of the action remains on this planet and the station that hovers above it.
The interaction with a translator from the powerful alien race known as the Presger proves to be significant but is also hilarious. The humor is present in this novel in amongst all the tea-drinking and possibly annihilation. That the book is funny despite the seriousness of the political maneuvering really makes this a more pleasant read than the middle book, which suffered from too much setup not to have a big enough pay off.
While there are worlds still out there to a explore, I believe Leckie pulled off a satisfying ending that rounds out what will go down as one of the most prominent science fiction stories of the decade. I'm surprised there was such shock at her using a single pronoun as it fit perfectly with the story-telling. I was wholly satisfied with the ending as Breq pulls off something very clever. I am excited that this book got chosen for a Hugo Award for best novel this year and will check out the other books to see how it compares!