Series numbering from spine.

"Ava hasn't found Tinabella to be the easiest roommate to get along with. She's sneaky. She's popular. And she bends the rules a lot when it comes to magic. Still, Ava never asked for Tinabella to be banished to a tower, trapped by a strange spell. And when the wickedest witch of them all attacks the School for Wicked Witches, trapping all the teachers within an enormous twister, Ava knows that it's better to have Tinabella by her side than to keep her locked away. Now the question is: With no teachers around, and even the oldest students in the school caught by the magic, what can Ava, Tinabella, and their friends do to prevent a truly wicked fate?"--