Breq is still juggling events on Athoek Station, and while all is not sweetness and light, there is progress being made on the repair of the Undergarden. Then the station's head priest of Amaat starts a work stoppage; she won't cast the omens, or register births, marriages, or deaths, until work on the Undergarden is stopped so there can be a "review" of how housing in the Undergarden should be assigned after repairs.
The wealthy and privileged are staging a counter-protest against the priests' work stoppage by forming physical lines at the station administrator's office. The formerly illicit residents of the Undergarden, whom Breq intends should be approved as permanent residents, stage their own clever counter-action: bringing food and drink to the people in the line. And while tensions are rising around this situation, four ships, almost certainly from the other Anaander Mianaai, gate into the system--far enough out that they clearly hoped to be unnoticed until ready to move.
And a search of the Undergarden turns up someone who shouldn't be there, who turns out to be an ancillary of a ship called Sphene, who has its own grudge against Anaander Mianaai.
And a new Presgar interpreter, Zeiat, arrives, wanting to know what happened to Translator Dlique.
It's all building toward an explosive crisis, but the real heart of the novel is the relationships. Sphene is cold and indifferent until it realizes that Breq is also an ancillary, or was, and has a very similar mission of revenge. Tisarwat is learning who she is, after being made Anaander Mianaai's ancillary and then being freed from that fate--not the old Tisarwat, not Anaander Mianaai, but with some of Anaander Mianaai's memories and knowledge--including the codes that give her override access to the ship and station AIs. Seivarden has been badly disoriented by waking up after a thousand years driftin in a suspension pod to find his formerly influential House gone. He's started to learn not to be so arrogant and so much of a jerk, but he still doesn't understand why certain behaviors, coming from his long-practiced arrogance, offend people. And he's left behind on Mercy of Kalr to command the ship while Breq is on Athoek. Seivarden is also markedly less emotionally stable when Breq isn't around. He manages to wreck his relationship with Lt. Ekalu, one of the few officers ever promoted from the ranks of the soldiers, with his arrogance and insensitivity.
With all this stress going on, these disparate people need to work together to fight the Lord of the Radch.
Things get more complicated, not less, as Tisarwat, on Breq's orders, frees each of the in-system AIs from Anaander Mianaai's control. Now the AIs can pursue their own agendas. Who, if anyone, will they ally with?
Woven through all this is Breq's slowly growing awareness that she's been doing to Mercy of Kalr and her human crew some of what she hated when it was being done to her.
Political intrigue, military conflict, and personal and interpersonal emotional growth and upheaval all mix together in to a novel that draws the reader in and keeps moving.
I bought this book.