This is the second book in the trilogy begun in last year's Best Novel Hugo winner, Ancillary Justice. Breq, having survived the confrontation between the two parts of Anaander Mianaai, is now in command of Mercy of Kalr, and off to contain another part of the spreading crisis at Athoek. While there, she hopes to also protect and offer some sort of compensation to the sister of her much-loved Lt. Awn, whom she was forced to kill.
At Athoek, she finds an already tricky political situation exacerbated by the closer of the gates and the news that there are at least two perfectly legitimate "Lords of the Radch" now in open conflict with each other. It takes longer to discover that underneath the existing and new political conflicts, and ordinary class conflict and exploitation, there's a truly horrifying corruption hidden here.
Did I mention there's another ship in the system, Sword of Atagaris, of questionable loyalties? And a little error in judgment by Atagaris' Captain results in the death of a translator/representative from the frighteningly powerful aliens, the Presger.
And while juggling all that, Breq is confronting her odd status as an ex-AI, ex-ancillary, now in command of a ship rather than a part of it. It's a sometimes unsettling experience for her, and at first her crew, except for old companion Seivarden, do not know what to make of her.
There's a lot going on here, in character development, revealing more about the history and culture of the Radch, and action as the conflict between the Mianaais and even older tensions in the Radch empire play out.
I'm looking forward to the third volume, Ancillary Mercy.