Killing Rites came out on Tuesday! I read it all in one gulp Tuesday night, and I'm still not sure I have much more coherent to say about it other than om nom nom right now.
The series is now at a stage where it's impossible to talk about the plot of the latest installment without spoilering prior books - even the back of this book outright tells you that Jayné has a rider. (I kind of think the series is more interesting if you read it already knowing that, though.) Killing Rites is about the attempt to get the rider out, the way in which that plan fails spectacularly, and how Jayné and the rider - the eponymous Black Sun's Daughter, finally brought to light - come to terms with each other.
I like the rider, actually. From Darker Angels, we know that beneficial riders are at least possible. From hints dropped throughout the previous books, we know that either this rider or its mother has been involved in very evil shit in the past - but as a slave, not necessarily out of her own inclination. She seems to be free of bondage from any of her evil brethren now; either she was released somehow, or the mother was the enslaved one* and this daughter has always been free and hidden away. It seems like one of her primary functions is to cast out other demons, or purify them somehow; in prior books, the word angel is thrown around, in the context of never met one or I don't believe they exist, and it comes up often enough that it seems significant to me. So I wonder if this rider is as close to an angel as you're going to get, and the other riders hate her and enslave her because they don't particularly want to go back to Hell.
But whether she's a good guy or not is outside the scope of this story - here, she's just trying not to get exorcised, just trying to survive. She acts like a good guy, and has consistently done so in the past, but it could all be a survival tactic. I think she's a good guy, though, and I'm looking forward to learning more about her later. (I hope she's OK; she has a rough time of it in this book. She's got to be at least OK enough, since the whole series is named after her... but this author employed his magic system to break the whole damn world in The Long Price Quartet - repeatedly! - so it's not like he's the sort to keep the gloves on and play gentle with his characters. She could very well be irreparably broken in some plot-driving way.)
I wish there'd been more Midian, though. The back of the book implied there would be more of that dude, but he really just passes through the story relatively briefly. Well, I can still hope he'll turn up again later. He's a very entertaining sort of lesser evil.
* I favor this option. If the mother rider was still enslaved, even up to the point of her death, it would explain quite a lot about Uncle Eric's behavior. But that might be just making excuses for him.