There are many alternate universes that branched off from each other, differing in many different ways. The most powerful enchanters and enchantresses of which there is only one in all of these universe holds the seat of Chrestomanci. Hermione is about to find out that that she is destined to hold the power to maintain the balance in all of these universes.

"On the one side, three wide-eyed teenagers, redolent of sweat and mushrooms, leveled pointy sticks with murderous hostility. Chant, on the other hand, could have been inviting them for tea after a matinee performance of The Magic Flute..."