The Order of Merlin Omnibus (Books 1-3)

Destiny calls when you least expect.
After five harrowing years in the Hundred Halls surviving dangerous supernatural threats, our group of young mages have each taken their own paths away from the university. But the recently returned Head Patron, Invictus, has need of their skills. Brought together under the banner of The Order of Merlin, these mages must survive everything their teacher throws at them—and each other—to become the team the world needs. Otherwise they don't stand a chance against the imminent demonic invasion.
This omnibus includes The Order of Merlin, Infernal Alliances, and Tower of Horn and Blood.