The Jasmine Throne by Tasha Suri

Imprisoned by her dictator brother, Malini spends her days in isolation in the Hirana: an ancient temple that was once the source of the powerful, magical deathless waters — but is now little more than a decaying ruin.

Priya is a maidservant, one among several who make the treacherous journey to the top of the Hirana every night to clean Malini’s chambers. She is happy to be an anonymous drudge, so long as it keeps anyone from guessing the dangerous secret she hides.

But when Malini accidentally bears witness to Priya’s true nature, their destinies become irrevocably tangled. One is a vengeful princess seeking to depose her brother from his throne. The other is a priestess seeking to find her family. Together, they will change the fate of an empire.