I enjoyed this more than I did the previous books in this trilogy (TITHE and VALIANT) and yet, still did not find it a satisfying read.
The good news is that there's more story to this. The impossible quest is interesting (albeit you can guess how it's going to play out pretty much the moment it's set) and you get more of a sense of the politics between the Seelie Court and the Unseelie Court. Luis and Dave make a reappearance from VALIANT, which I thought was well handled, especially because of the way it built on Luis's role as a fixer whilst further developing the relationship between the two brothers.
The best parts of the book though are those that focus on Corny. The character is a like a walking open wound - still grieving the death of his sister and recovering from his own experiences at the hands of the Unseelie Court, he's terrified by faeries and by his own vulnerability to them and that makes him determined to never give them power over him. In many ways, Corny is the most dynamic character in the book, he's the only one who is actively trying to take control of his own destiny and whilst he sometimes gets infected with Stupid Decision For Stupid Reasons Syndrome. When Corny brings a powerful curse down on himself at the hands of a faerie, it's a twisted blessing in disguise as it finally gives him the means to hit back at the faeries who would torment him and I think that Black does well to handle the exultation and despair that the curse brings him, even if I would question the means by which Corny and his friends try to deal with it as being slightly too contrived.
Unfortunately, the big problem remains Kaye. Just as in TITHE she is a reactive and passive character, always being tricked or manipulated by others so when you get to the scene where she finally stands up for herself, you really don't believe it. The scene where she confesses to her mother about her being a changeling should have been powerful and yet because you can guess how it's going to play out (not least because Kaye already knows how it's going to play out), it lacks the punch it needs. I also found that I just couldn't believe in the relationship between her and Roiben. Whilst I can see what she sees in him (in that whilst he remains underveloped and two-dimensional, he at least has a certain enigmatic quality), I couldn't see what he saw in her, which ruined the true love element that supposedly exists between them.
There are some powerful scenes in the book, notably the attack on the Unseelie Court, which I thought was well handled. I also continue to admire Black's skill in creating sensual and lyrical images - particularly where she describes the effect of the city on faerie folk. Unfortunately, the downside of this is to reinforce how superficial the story ultimately is and I was left wanting to see more expansion on themes and especially on the politics between the courts and the rivalries that drive it. Given the cruelty displayed by Silariel at almost every opportunity, why are her courtiers so loyal to her? Ethine would have been the perfect character to explore this, given that she's used as a pawn just as much as Roiben, and yet she remains unquestioning throughout, which I found frustrating.