The traditional middle-book problem is that the protagonist doesn't have a lot to do except suffer a disastrous, cliffhangery setback on the last page. This is not that book. Duchess gets into a whole stack of schemes, from guild politics to sabotage to undercity explorations to good old-fashioned heists. Some of them she starts; some just happen to her. (Some -- both.)
The city remains interestingly multileveled, and I mean that in every sense. There are alley-trawling thugs and high-society grandees and everything in between, but the interesting interactions are between the layers. The whole backdrop of this series is the War of the Quills, where a nobleman tried to change the political balance of the city by arming low-city bully-gangs, and it went... poorly. That history looms large in this book's story, too.
Duchess is not as extravagant or as dramatic (or as foul-mouthed) as some of the fantasy thieves we've known, but she's got a nice mixture of determination and naivete. (All her schemes are clever; none of them come out exactly the way she intends.) So I will stick with this.
I find that I now visualize Lysander as Jordan Gavaris in a blond wig. Perhaps you will have this problem too.
Looking back at my previous review: Yes, this book gives us a much better perspective on the Grey. On the other hand, I didn't feel entirely up to speed with the events of the previous book (which I read more than two years ago). So there's a general pattern of the authors not being quite good enough at inclueing important background. (I suspect this is a risk of the self-publishing world; experienced editors catch it.) If you read the books together, of course, this will be less of a problem -- but then you get to wait with me for book three. So it goes.
(Interest: I had dinner with Daniel Ravipinto and he handed me a free copy of the book.)