Grey Griffins: The Clockwork Chronicles No. 3: The Paragon Prison : The Clockwork Chronicles #3:

In this, the third book in The Brimstone Key Trilogy, Avalon Academy's turbulent first semester is winding down. The students are trying to find a balance between cramming for final exams and practicing for the Round Table qualifying tournament. But for the Griffins, the joy of the holiday season is being overshadowed by the return of The Immortals, and the escape of a changeling bred to detonate like a nuclear bomb.