City of Stone and Silence by Django Wexler

After surviving the Vile Rot, Isoka, Meroe, and the rest of Soliton’s crew finally arrive at Soliton’s mysterious destination, the Harbor—a city of great stone ziggurats, enshrouded in a ghostly veil of Eddica magic. And they’re not alone.

Royalty, monks, and madmen live in a precarious balance, and by night take shelter from monstrous living corpses. None know how to leave the Harbor, but if Isoka can’t find a way to capture Soliton and return it to the Emperor’s spymaster before a year is up, her sister’s Tori’s life will be forfeit.

But there’s more to Tori’s life back in Kahnzoka than the comfortable luxury Isoka intended for her. By night, she visits the lower wards, risking danger to help run a sanctuary for mage-bloods fleeing the Emperor’s iron fist. When she discovers that Isoka is missing, her search takes her deep in the mires of intrigue and revolution. And she has her own secret—the power of Kindre, the Well of Mind, which can bend others to its will. Though she’s spent her life denying this brutal magic, Tori will use whatever means she has to with Isoka’s fate on the line…