The fire queen

"Though the tyrant rajah she was forced to marry is dead, Kalinda's troubles are far from over. A warlord has invaded the imperial city, and now she's in exile. But she isn't alone. Kalinda has the allegiance of Captain Deven Naik, her guard and beloved, imprisoned for treason and stripped of command. With the empire at war, their best hope is to find Prince Ashwin, the rajah's son, who has promised Deven's freedom on one condition: that Kalinda will fight and defeat three formidable opponents"--Amazon.com.