It's the end of the year for the student witches, and Mildred's incantations still don't seem to work as well as intended. To cure a case of hay fever brought on by one of Mildred's errors (""Exfoliatus!"" ""A CHOO!"") the other teachers give Miss Cackle what they assume to be a remedy potion, but which is in fact a mislabeled experiment of Miss Hardbroom's. The other teachers make no mention of the mishap, even when Miss Cackle's behaviour takes a turn for the malicious. It is Mildred and company, however, who realize that it is not Miss Cackle, but her evil twin back to cause more trouble. Mildred saves the day, for which she earns a raise in her final grade from C-- to A+.