Lotte and Thijs go to a great school and have a sweet teacher, Miss Evi. But then the awful Miss Brakel becomes principal and makes all sorts of rules: no phones, birthdays are no longer allowed, and treats are strictly forbidden. So the class gives her a nickname: Miss Vomit. They devise a plan to get rid of her, while Lotte also has a secret that needs solving. Can Miss Evi's magic ring help?

Miss Vomit is back! She keeps coming up with new horrible rules and all the best friends are being separated. That can't happen, can it? Lotte and Thijs want to do everything they can to unmask her and chase her out of school. Together with Miss Evi and her magic ring, a mysterious compass and Vomit's scary friends Greta and Alie, they have to stop Miss Vomit! Until Lotte and Thijs themselves are captured. Will they manage to escape in a brilliant way?