Following the rebellion against Cackle's Academy, Mildred and Jadu have been suspended from the school. Until their parents come to collect them they are forced into isolation, copying out chapters of the 'Historica Magica'. Maud decides she will run for Head Girl to get Mildred and Jadu reinstated back in the school, but realises this won't be easy when she discovers that Ethel is also running.
Miss Drill complains to Miss Cackle about giving Mildred and Jadu the chop. She says Maud's running for head girl. Miss Hardbroom says that Ethel's going to win. Miss Cackle hasn't mailed the letters to Mildred and Jadu's parents yet. Miss Hardbroom offers to, but Miss Drill says to hang onto them for a day and see how she feels about it later. They have a tug of war until Miss Cackle snatches them back. Drill and Crotchet want to make sure Miss Hardbroom doesn't fix the election, and they talk Cackle into magically locking up the ballet box.
Mildred draws a drawing of Prince Percy who fought a dragon (as they read while copying books) and she and Jadu watch thunderstruck as he comes to life on the page. When the dragon comes to life they bury the paper under heavy books.
At the end of class, Miss Hardbroom basically tells everyone to vote for Ethel. "If she's saying that to all her classes, Mildred and Jadu haven't got a chance." They cast a spell that lets them look back in time, and they remember how Mildred's always saved the school from disaster when she was in real trouble. Maud decides to go talk to Fen and Gris.
The girls have the idea that if Mildred had the opportunity to save the school from destruction, as she had done before, then it would count in her favour and Miss Cackle would reinstate them. They then decide to summon a mythical monster from a dangerous book called the 'Mytheocopia' with the intention that Mildred and Jadu would save the day.
Fen and Gris help them get the book, which Miss Cackle keeps in her office, behind the wall, and you need a password to get into it. And if you don't have the password, a cage drops down on you until she says the password again. And she changes it every week. "How do you know this?" "Don't ask."
Miss Cackle's just sending Ethel to mail the letters for her when Drusilla runs in and says that an alarm in her office just went off. Miss Cackle goes running down the hall, saying how it could be an evil witch or something. She goes into her office and says the password "Cauliflower Cheese", but it's only Tabby in the cage. She picks up the cat and leaves.
Maud turns visible again just then. Drusilla and the others come in, and they get the book. They decide to summon a Unicorn, and give Drusilla the antidote (it's a song you have to sing to it). She takes it up to Mildred and Jadu.
However, the plan goes horribly wrong when they accidentally summon 'The Uninvited'- an evil witch who sets about putting everyone in the castle into a deep sleep. Ethel is frozen just as she's about to open the front door, letters still in hand.
The Uninvited finds Miss Crotchet by herself, laughing about Mildred's drawing, and some of the jokes in the paper. "You think it's funny do you?" She freezes Crotchet's arm, and demands to know where the princess is. Meanwhile, Mildred discovers she has the ability to bring her drawings to life, she brings her drawing of Prince Percy off the page.
Mildred, Jadu and Drusilla then use Prince Percy to wake everyone who has been put to sleep with a single kiss to the lips. After waking Miss Hardbroom, they proceed to the Great Hall where The Uninvited has just put Miss Crotchet to sleep. Miss Hardbroom battles the evil witch but is overpowered, and it is left to Mildred to save the day by returning The Uninvited to the Mytheocopia using her special ability.
The prince wakes everyone else up, and Cackle asks Mildred to put the prince back on paper. She does. "Amazing!" Cackle calls Mildred away because she wants to talk to her. Miss Hardbroom looks after them, "Imagine that girl with such a talent." Ethel interrupts, saying that she's going to mail the letters. Miss Hardbroom casts a spell on them when she's not looking.
Later at the Head Girl election, Maud gets up to make her final speech. She says she doesn't want to be head girl anymore. She wants Mildred to be. She asks who else wants Mildred and Jadu for head and deputy-head girl. Everyone but Ethel does.
Miss Hardbroom says that the letters have already gone out, and Mildred and Jadu aren't pupils there anymore. Ethel says that when she went to mail them, they wouldn't come unstuck from her fingers - like someone had put a spell on them. ("I can't think who would want to do that," says HB) Miss Hardbroom says that it would reflect poorly on them to have a head and deputy-head girl who were expelled. Miss Cackle agrees and reinstates both of them, and makes Mildred Head Girl and Jadu Deputy Head Girl in recognition of their efforts in saving the Academy once again.
Miss Crotchet: (Reading Unfairground newspaper out loud.) "Question: Why couldn't Enid Nightshade open the door to chanting class? Answer: Because she couldn't find the right key." (Laughs.)
Uninvited: "Think it's funny do you?"
Miss Crotchet: "Well yes actually -"
Miss Hardbroom: "No Miss Cackle, I have never, ever seen anything like it. Who would have thought that girl ... would have such a talent?"
Miss Hardbroom: "In my judgement, Miss Cackle, it would not benefit the reputation of the school for the head girl and deputy head girl to be two suspended pupils of this establishment."
- The Uninvited witch drawn from the book is based on the witch from the tale Sleeping Beauty. Indeed, the witch points out she was not invited to a christening, comments on the pricking of fingers and puts nearly the entire school under a sleeping spell.
- When Enid, Maud and Drusilla consider bringing a Unicorn out of the book to help save Mildred and Jadu, Enid blurts 'Well don't ask me!' when they suggest singing. This is reference to her (supposed) bad singing ability. Enid's singing is also referenced in a joke Miss Crochet reads from 'The Unfairground' newspaper.
- This marks the final time we see Miss Hardbroom breaking school rules. She displays a dry sense of humour at the end of the episode.
- The second chorus of the school song is played whilst the episode is still running. This previously happened in Season 2.
- Fittingly for the very last episode of the show, the show ends in the sunset.
The Worst Witch TV Series