First 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. 
 In this book, wizard Felix Harrowgate's past returns to force him to destroy the magical focus of the city of Melusine, an artifact called the "Virtu." He goes insane, but eventually meets up with his half-brother Mildmay, a former assassin on the run from the law, who takes him on a quest to the one place that can restore him. 
 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.