Kinda like the first book in the series – a lot of very cool worldbuilding, but … kinda too much coolness and not enough substance. If you look behind the window dressing, it’s kinda just Omelas, yet again.
Don’t get me wrong: It’s pretty. The writing is alright, the people are at least somewhat compelling, and I enjoy puzzling out the overly in-depth worldbuilding. But it also feels so very hollow (and why on earth is there a third part?).
Beware: full spoilers! Also probably incomplete and possibly incomprehensible.
Brezan is a Kel officer, a crashhawk (meaning he can choose to serve, because formation instinct doesn’t take him). He’s also a womanform, so ~trans, kinda. General Khiruev is his commanding officer. Kel Cheris comes aboard (refer to the first book for details on the Kel), and presents herself as Jedao. She takes over the fleet and sends everybody lacking formation instinct away. She then takes up the battle against the Hafn. Khiruev tries to kill her against formation instinct and fails.
Meanwhile, we also see a lot of Hexarch Mikodez. He has a brother who he uses as a double, and a very committed second-in-command, and also a terrifying reputation, which, while deserved, is also carefully curated. He and the Kel hexarch are the only ones not interested in the search for immortality that the other hexarchs are pushing (in order to get even with the Nirai hexarch who is already immortal).
The Hafn are a weird human-alien culture using plant-hybrids for energy. They find lots of small sentries with dead children covered in different plants along the border. The hexarchs meanwhile decide to gamble on Cheris still being in there somewhere and try to blackmail her with genocide against her super tiny minority people. Mikodez has as many of them rescued as possible.
Brezan is sent to kill Jedao, along with the daughter of the Andan hexarch, as a high general (to override formation instinct). Well, turns out everybody is tired of the hexarchate and the torture and stuff, so nobody really wants to oppose Jedao individually, so even Brezan gets with the program. But before that, Khiruev got orders from central command to act against Jedao and decided not to. Kel command can do that – once, it starts a 100 day timer to their death.
Cheris retreats for a while and does math magic to figure out how to change the hexarchate calendar to make it so that only willing consenting people can interact with the calendar and its resulting magic, but remain compatible with most old tech. It all comes down to choice – that’s why Cheris also lets Brezan walk freely in the fleet to figure out what’s going on. They just need to kill all the hexarchs to do it (though Mikodez survives, prewarned, because his brother insists on going in his stead.).
Cheris does some final propaganda and espionage thanks to the servitors, has Kel Command attacked, and kills the hexarchs. Khiruev manages not to die, btw, by choosing not to. Also some final “Jedao was never mad, he wanted to dismantle the system”.