Before the Devil Breaks You by Libba Bray (Diviners #3)
After battling a sleeping sickness, The Diviners are up against a group of new and malevolent foes; ghosts! Out in Ward’s Island sits a mental hospital full of lost souls from people long forgotten. Ghosts who have unusual and dangerous ties to the Man in the Stovepipe Hat also known as the King of Crows. With terrible accounts of murder and possession flooding in from all over New York City, the Diviners must band together and brave the ghosts haunting the asylum to bring down the King of Crows.