 It is nearly the end of Mildred s first year at Cackle s Academy. One night, there is a strange, fierce wind which blasts through the castle, rattling and shaking everything and giving Mildred and Maud bad nightmares. Next day, everything seems fine - except for Miss Cackle. She seems completely out of sorts. She is particularly irritated with Mildred and actually tells the staff that she is the Worst Witch in the school and that she is going to expel her. Miss Hardbroom is pleased to hear her opinion of Mildred confirmed, but strangely piqued about the expulsion - she finds herself saying there is little point in doing it now. When Miss Bat reminds Miss Cackle how Mildred saved them all from her wicked sister, Agatha, Miss Cackle breaks into a fury and says that relations between her and her sister are of a private matter. Mildred is put in isolation for the night, and spots Miss Cackle waving a lantern towards the forest. Mildred, Maud, and Enid consult as to what it means - has Miss Cackle been magicked by her evil sister? Mildred thinks not - witches aren t allowed to revenge themselves once beaten. Luckily, Ethel, who has followed them, knows about a statute of limitations - and Agatha s will be up at the high noon on the last day of the term. Ethel feels a bit sorry for Mildred now that she s going. It takes all the combined resources of the first years, to discover what is really going on - of course, Miss Cackle is her sister, the wicked Agatha! The girls track down the real Miss Cackle to the store cupboard in which Mildred and Enid were once trapped. Unfortunately, they are discovered by two of Agatha s wicked cronies, and time is ticking away to midday on the last day of term. The final confrontation takes place in front of everybody and gives Mildred a chance to show us all why she s really the best witch in the school.