Gathering of Shadows: The Hundred Halls Series Book Four

Every fall the city of Invictus bustles with new students, and the classrooms reek of spent faez. This year it's true of every hall except one-Arcanium. While Semyon Grey, the Patron of Arcanium, slowly heals from his soul being torn, no one in the Hall can practice their craft, leaving them defenseless against the Cabal and faez madness. The Silverthorne sisters must find a way to speed up the healing, or the Hundred Halls won't survive the year. But everything they try only makes things worse, until they're left with an impossible decision that may cost the sisters their lives.