Out of Bounds is the twelfth episode of The Worst Witch (2017 TV Series). It was first broadcast on CBBC and CBBC HD on 22 March 2017. It is preceded by The Mists of Time, and followed by The Worst Headmistress.
Mildred messes up a growth spell, shrinking herself instead of growing. Miss Hardbroom reminds the class that exams are coming up, and students must pass the exams to continue at the Academy. Mildred then receives a message from Miss Cackle, requesting a private conversation. Mildred meets Miss Cackle in her office, and they discuss the birth scroll (from the previous episode) which reveals Agatha is actually older, and therefore the rightful head of the Academy.
Maud gets mad at Mildred for not studying with her, while Miss Cackle goes to check on Agatha, only to find that she's escaped from the cottage where she was banished. Ethel, wanting to know what the secret is between Mildred and Miss Cackle, makes a potion to disguise herself as Maud. When Tabby acts strangely toward Maud, Mildred and Enid Nightshade realise that it's Ethel in disguise, and Mildred tells her the fake 'secret' that she's Miss Cackle's niece.
Miss Cackle contacts the Grand Wizard to tell him that Agatha has escaped, while Miss Hardbroom puts protective enchantments on the castle, so that no one can get in unless they are invited, and students are banned from leaving the school grounds. In potions class, Ethel makes a friendship potion and tries to get Mildred to take it, resulting in a fight. Miss Hardbroom takes them to Miss Cackle's office, where Ethel says Mildred told her she was Miss Cackle's niece, and Mildred says that Ethel was pretending to be Maud at the time, resulting in both of them being confined to their rooms.
Mildred thinks that Agatha is pretending to be Miss Cackle again, and Maud tells Mr Rowan-Webb and Miss Bat. Maud then takes Rowan-Webb (turned back into a frog) to Miss Cackle and says he needs changing back again, as Agatha had her magic removed and wouldn't be able to do it. However, Miss Cackle turns Algernon back, suggesting that she isn't Agatha.
Mildred isn't convinced, though, and, despite the restrictions in place, flies to the cottage where she thinks Agatha has trapped Miss Cackle. 'Miss Cackle' claims Agatha has taken her powers and tries to get Mildred to give her hers, but Mildred realises that it's actually Agatha. Miss Gullet appears and vanishes Mildred's broom, but Mildred escapes and returns to the Academy on foot.
Meanwhile, Ethel sneaks into Miss Cackle's office, followed by Esmerelda, who wants to know what her sister's doing. They find the birth scroll, and learn about Agatha's birthright. Agatha and Miss Gullet then turn up at the window, and claim that Agatha is Miss Cackle. Esmerelda invites them in, and is tricked into giving Agatha her power before Miss Cackle comes in and she realises what she's done- but Ethel knew it was Agatha all along.
Agatha takes over the school, and Miss Drill is turned into a snail when she tries to stand up to her. Mildred finally gets back to the Academy, but Maud tells on her to Miss Hardbroom, and Mildred is Expelled and sent home.