A Reaper at the Gates by Sabaa Tahir

In a thrilling sequel to A Torch Against the Night, Sabaa Tahir returns to the world of Laia, Helene and Elias with A Reaper at the Gates. In Reaper, the stakes have been raised for all our favorite characters as the Nightbringer draws closer to his goal.
In the Waiting Place, Elias struggles to take control of his growing powers as Shaeva and Mauth force him and Laia farther apart. At the heart of the Empire Helene has taken control of the Black Guard— and with Harper at her side begins to wrest control from the Commandant. Far away, Laia works with the Tribes and Scholar Rebels to free enslaved Scholars.
But even as the Blood Strike grows in power and Laia gains allies and experience, the Nightbringer too grows closer to freeing the other Jinn. Under his orders Keris Veturia schemes and kills as she works to undermine the new regime.

Reaper at the Gates is probably my favorite book of the series yet. The POV characters have gained a new maturity since the events of A Torch Against the Night, and many of the supporting characters also gain a backstory that helps to enrich the world of Reaper comsiderably.