I have to say I didn't try very hard. I read the first chapter or two and then gave up because it was incredibly confusing, despite the fact that I'd read the first two books. But I'm kind of glad because I kind of hate myself for liking this series so far.
The book claims to be denouncing torture. The protagonist, Andrej, the torturer himself, believes this as the narration says blatantly on page 15, "Torture is terrorism." There is some discussion of the horror of torture. But the books aren't about torture. There's a murder mystery in here. Which is just disturbingly mundane when something so horrific as institutionalized torture is occurring. The books are also about what torture does to the torturer who opposes torture to an extent. Except that he hates it until he starts doing it and then he enjoys it and he hates this about himself. And then he emotionally punishes himself. Poor torturer. Somewhere (I can't find it now) someone says he is as tortured or more so than the souls he punished. Hunh, really? How about the ones he tortured at level 10 (the highest) which is to the death? This is institutionalized torture, with levels and protocols requiring the torture to go through levels before getting to the top level and death. Even the lower levels usually take days. Oh yes, much better to be the one on the rack, right?
There's no doubt in my mind that Matthews is a gifted storyteller and that she writes well and creates a convincing future world. It's a horrible universe, one that has no redeeming value that I can see. There isn't any hope, no real uprisings, no one going against the regime. And that makes a very bleak world to read about. The people are mostly icky, too, self-serving and power-hungry with the exception of Andrej's slaves, who pretty much worship him. (He's very wealthy but not allowed to buy out their bonds.)
So this time, for the first time, she tries to have some comic relief by inserting an elderly bat-like creature who has a gift for cunning. She doesn't really do aliens as well as some other things. And the humor is just not appropriate or maybe not appropriately applied. The subject is just too heavy for this humor to work. The moments with this creature felt like fan fiction, an oddity in this work that uses a very formal voice to fit the very formal environs.
It is frustrating that, even for SF, there is too much not explained in the first chapter to get more than a general idea what's going on. Many times I had to reread passages to even follow what was happening and I was still confused when I stopped.
The book probably does improve as you get into the mystery and figure out what they heck they're talking about. But frankly, I just don't want to give time to this awful world and this horrible situation. We got the point in the first book. More were unnecessary.