The Sheriff of Nottingham and Guy take over Hogwarts, and Robin's gang teams up with Harry's to regain control of the school. Alternative reality with dystopian Canada. Many cross-overs.
I can't wait to know more about Season 3, so I'm writing fanfic in anticipation. This is set 4 years later, like the next series will be. The main characters still suffer the consequences of their actions last time around, and everyone wants a revenge.