This is not a good book. It is, however, incredibly engaging on a very specific level. If you're looking for reasonable human beings, beautiful turns of phrase, thoughtful politics or believable dialog, this is not the book for you. BUT. If you want melodramatic wish-fullfillment crack, then the only series more suited is Lackey's The Last Herald-Mage.
This is the latest book in Bishop's Black Jewels series. The world is split into two classes: the downtrodden landen (basically serfs) and the Blood, who do magic and have ruled the world for centuries. Blood operate in a very structured hierarchy: those with more magic rule over those with less, and every member of society grows up knowing exactly what their place is. Territories are ruled by Queens, who have a tangled sort of feudal relationship with their Courts of male Blood. Over the centuries, this hierarchy became twisted and malformed, and many people lost their lives or sanity to the sadistic whims of those in power over them. The heroes of the first trilogy, Lucivar, his half-brother Daemon, and their Queen, Jaenelle, all suffered through torture and slavery before finally destroying the most dangerous members of the Blood. Two years later, they are still dealing with the fall-out. Daemon has never quite recovered his sanity, and Jaenelle no longer rules. And despite Jaenelle's best efforts, many territories are still in revolt against the Blood.
Dena Nehele is a provincial backwater, but when the descendent of Jared (from The Invisible Ring) requests help, Jaenelle makes sure to send the person best suited for the job. Cassidy is not beautiful, magically powerful, or aristocratic, but she is a Queen, and she has the right instincts for the job. Her journey toward becoming a true ruler, and her Court's journey to accepting her rule, takes up much of the book.
The usual problems with Bishop apply here. Her books rely upon gender essentialism to an almost unbearable degree. People have inborn rank and power, and going against it is a terrible travesty. Sexual violence, slavery, and violence are talked about on every page, although everything happens either off-screen or before the book begins. The plot is wrapped up poorly. The romance is nontraditional (and actually, about as sketchy as Daemon and Jaenelle's) and not that believable. And yet somehow, I couldn't take my eyes off the pages.