The Sorcerous Spy — Thomas K. Carpenter

When a rogue assassin starts taking heads in the Hundred Halls, no one is safe, not even the teachers.Zayn leads his team as they investigate the gruesome deaths. The search draws them to dangerous places: the infamous Black Council and the opulent casino of pain run by the Diamond Court. As leads dry up, and heads roll, leaving them no closer to the truth, Zayn must make a terrible choice involving the people who he cares about most.