Blood of the Four by Christopher Golden and Tim Lebbon is the story of the kingdom of Quandis. Phela, second in line to the throne, suspects her mother Lysander of using magic, forbidden to all except the highest level of priest. But Lysander is ambitious, as is Phela herself.
On the other end of the social hierarchy are the Bajumen, the most lowly of slaves, hated by all. But Bujumen can elevate themselves by joining the priesthood, as has Blane. Blane also has ambition, but his is noble, the freeing of his people.
As the story progresses, people of all classes (royalty, nobility, priests and slaves) are called upon to take sides, as both Phela and Blane become more powerful, in a battle for control of the kingdom and its magic.
Blood of <the Four is a page-turner, following the journeys of several characters during the difficult times. It’s definitely worth a look.