Third in a series featuring a tortured wizard and his former-assassin half-brother, as they go around causing trouble, being exploited, destroying magical artifacts and restoring them, and exploring all the magical implications of labyrinths. 
 Now, this is a transitional book in which a whole lot of nothing (or, if you prefer, court intrigue) happens. So if you like court intrigue (which I do), then you'll like it; otherwise it's going to seem a bit slow. There's also a third protagonist, the actress/spy character Mehitabel Parr, in this book, whose perspective really made this story interesting. 
 I really enjoyed the world-building in this series, the characters (I'm a sucker for a tortured hero, and Felix and Mildmay are literally and figuratively tortured), the adventure, the intrigue and the way the author doesn't yield to temptation to make the magical systems all neat and tidy. I recommend this series highly.