I think I understood about 75% (maybe 80%) of what the hell was going on in this book. About 25% I can sort of infer or just assume "SPECIAL THING THAT GOES BOOM".
Saying that, it was very enjoyable. It did take about reading 40% of the book to really get a grip on the world/universe/science. I don't even know if I can explain the plot.
Most of the story takes place in a post-human society on Mars. People live a normal 'human' life for a time, before becoming the brains of things that build and maintain their city on Mars (called the Quiet). When they've served their time, they get some time to live normal lives again. There's also others that do things differently, different types of humans that aren't from Mars but are also generally post-human. It's complicated.
The main story is about a thief, trying to get his memories back. In turn, he has to help the person who rescued him from prison to steal something else.
There's also a detective, trying to solve various mysteries for different people on the Oubliette (the city on Mars). They all intertwine at the end and it makes sense...sort of. Even one of the big moments (I thought in the book) only made some sense to me after reading the whole book. I imagine to everyone else, it looks like meaningless gibberish:
Isidore takes a deep breath. 'An interplanetary thief is building a picotech machine out of the city itself while the cryptarchs take over people's minds to try to destroy the zoku colony in order to stop the tzaddikim from breaking their power,' he says. 'I want to stop them both.' He pauses. 'Also I think the thief is my real father.'
It is pretty amazing though, the complete world building and completely different society that has emerged. It reminds me a lot of Ancillary Justice in that it is recognisably human, but just. There's enough to keep you anchored but if you don't pay attention, it would get away from you.
But it is good. It's better than a lot of science fiction that I've read lately. It has lots of women (though, the thief does outsmart at least 2 of them at one point). But they are all powerful, intelligent, self-reliant, complicated and their own characters. That was wonderful. There's even more diversity, not all the characters are either white or straight! Also a ship with a personality, which is a thing I always enjoy.
I think I'll give it a 4/5. It does lose 1 star because I'm uncertain whether I've even understood it. Though, I am going to pick up the sequels.