On their first day, Mildred's phone is confiscated by Miss Hardbroom. The first years are assigned their houses and Maud is made head of the first year. The first years receive their cats and have their first flying lesson. Mildred's cat, Tabby, is scared of flying and Tabby causes her, Maud and Ethel to crash into trees. Miss Hardbroom decides to arrange a flying test for the class and Ethel tells Esmerelda she will help Mildred. When Mildred tries to train Tabby, Ethel offers to help and pours some sardine juice on the broom tail. Ethel and Mildred pass their tests, whilst Maud crashes because of Midnight, however, Miss Hardbroom reveals Mildred and Maud's cats have been switched. Mildred is told her trial is over as it is assumed she cheated on her test by switching her cat with Maud's. Mildred and Maud try to find evidence that Ethel was responsible and they find the sardine tin. They both decide to try it and they switch bodies - the juice contained a switching spell. Just as they are coming to terms with what is happening, Miss Hardbroom arrives. Maud, with Mildred's appearance, is sent to Mildred's room by Miss Hardbroom, unbeknownst to her. The following day, Miss Cackle finds Tabby with a notebook belonging to Ethel that contains a list of ingredients for a switching spell. Ethel admits to switching the cats, but says that it was to help Mildred pass her flying test, and Esmerelda backs her up. Ethel is forgiven and Mildred is kept on at the school, still on a trial basis. To pass her next flying test, Mildred uses her satchel to carry Tabby, which Miss Hardbroom scorns, but Miss Drill and Miss Cackle think is a clever compromise.
Esme: See your sash?
Maud: Yeah. What does it mean?
Esme: It means you came top in the entrance exam, and so you're head of Year One.
Miss Hardbroom: To be slightly more accurate, you are the least worst.
Miss Hardbroom: Do you know what a witch is, Mildred Hubble? Do you know what a witch does?
Mildred: Erm... Spells? Broomstick flying? Wears a pointy hat?
Miss Hardbroom: A witch takes responsibility. A witch does not whine when things don't go her way. A witch makes things go her way.
Maud: Wow, Mildred, you did it! You're the bats. (pause) That means you're good.
Mildred: I'm the bats!
Mildred: So somebody else must have done it.
Maud: No prizes for guessing who.
Mildred: Ethel? But she was nice to me yesterday.
Maud: Well, that definitely counts as suspicious behavior.