As others have mentioned, this may be Book 2 of the Viscount trilogy, but it's actually book 4 of a series, and you DO need to read the previous 3 in order to appreciate this one.
I have noticed, as time goes by, that there is a pattern to opinions about the Khaavren series: those who started reading Steven Brust's Vlad Taltos series first, and bought one of the Khaavren books because it was by Brust, don't seem to appreciate the Khaavren books as much. Those of us, on the other hand, who started on Brust with this series, or with some of Brust's other fantasies entirely, seem to enjoy the Khaavren books more. I believe it's a question both of writing style, and of one's definition of action. Thus, if you really, really like the Vlad Taltos books, and you expect these to be similar, it may be that you will be less than enchanted with these.
I believe that those who have read a lot of older literature - Dumas, as many have mentioned, and definitely Shakespeare - will enjoy this book, and the Khaavren series, more than the Vlad Taltos fans will, on average. (Of course, every reader has a unique background and a unique perspective - don't let me stop you from reading!!) Certainly a background of the Three Musketeers (and not the movie, people!) helps one appreciate what's going on here - but a knowledge of, say, the battles in Shakespeare's Richard and Henry plays, does not come at all amiss. And a comfort level with the intricate language of Shakespeare, as well as the overwrought prose of Dumas, gives one the stamina to follow Paarfi's extensive perorations.
Let me also mention that there's a dash of Romeo and Juliet in here, with lovers from different houses and their disapproving families. Those who feel that there is not enough action in this book, apparently do not consider a good heartbreaking love story to be action. But it is! So is the evolution of the magic taking place - if moving hundreds of warriors via magic/mental powers, over hundreds of miles, which has never been done before in this world, is not action, then what is? There are no slow moments if one is interested in emotion and magic as well as in swords and battle; there is always something happening between people.
As with previous books in the series, if you do like it, it has an effect on you: you talk funny for days afterward, if not weeks! Hey, if you are planning on taking the GREs or GMATs, this series is a terrific vocabulary builder!! There will be nothing in the verbal section that you can't handle, if you enjoy and appreciate Paarfi!
In short - if you already like this series, this volume is a must; if you like Dumas and Shakespeare, you'll like this; if you like Vlad Taltos, then start in on this series in cautious, easy steps.