The Immortals 03 - Emperor Mage by Tamora Pierce

Emporor Ozorne’s Immortal minions have savaged peaceful Tortall. Now Ozorne talks of treaties, and for Tortall’s sake, Daine must attend the peace conference – somehow keeping her wild magic in check. But other forces demand she unleash that power. The Gods are furious with Emperor Ozorne, and have chosen Daine to deliver their dreadful retribution. Compelled by the Graveyard Hag, Daine confronts Ozorne. But should she use divine power to bring the mighty Empire to its knees…?