Root has persuaded Miss Cackle with a certain amount of blackmail concerning the girls' behaviour in the village to allow the gardening competition to take place in the Academy Courtyard. She is given the task of taking the Third Year potions class, but she is immediately thrown in at the deep end by Miss Hardbroom, who makes the Third Years out to be wild, uncontrollable rebels. The growing potion turns out to be the right answer for both Mildred and Mr Blossom, while Ethel's plans blow up in everybody's face. He escapes to the kitchen where he is in equal danger from Mrs Tapioca's cat. All seems to go well until the Grand Wizard arrives with Baz and Gaz and demands a traditional English tea. She then discovers she has the ability to bring her drawings to life.
It is then revealed that Gabrielle is Miss Cackle's niece, but Miss Hardbroom insists that she should be treated like any other student teacher and plans to test the Third Years on what they have learnt with Gabrielle. Mildred goes down to the basement armed with a walkie-takie, and Baz and Gaz start fighting over her. Mr Hallow arrives at the academy and convinces the teachers to set up a computer system. However, this leaves little time for Mildred to spend with Maud. The girls meet a nature-loving businessman named Sam, who has trouble standing up to his overbearing boss. For once Ethel and Drusilla team up with Mildred and her friends.
Charlie's hopes are dashed until Fenella and Griselda turn up with a book, which states that every boy who turns up at the founder's day feast must be automatically accepted into the Academy. Most episodes revolved around the school, following the adventures of Mildred and her friends. Meanwhile, Mrs Tapioca is having problems with a rat in the kitchen. However, the spell goes wrong and Mildred ends up being transported back to the school, where she finds herself hanging from the chandelier in the Great Hall where some of the girls are rehearsing for Miss Cackle's celebration. Miss Drill and Charlie Blossom are the stage managers, but Charlie accidentally destroys Miss Hardbroom's pumpkin just before curtain-up.
Mildred thinks this is all Miss Hardbroom's doing, when she is unceremoniously dumped into a jar. With a heavy blizzard raging, Miss Drill suspects magic and begs Miss Hardbroom to stop the weather, but it takes a bit of convincing. The other teachers make no mention of the mishap, even when Miss Cackle's behaviour takes a turn for the malicious. Meanwhile Miss Hardbroom is fed up with Miss Bat's irresponsible attitude to teaching and her habit of eating flowers. But Miss Hardbroom is convinced it will all end in disaster and resolves to have nothing more to do with the trip.
When Ruby mentions that it might be possible to do so, she modifies a pinball machine into a time-traveller. Maud is playing Cinderella's wicked stepmother, and her character is dressed as Miss Hardbroom. As Miss Cackle evacuates the Academy, Mildred asks Miss Hardbroom for help, claiming that she has a plan to discover which is the real Lucy Fairweather. Mildred and her friends decide to make a stand against the rules, and they have some unexpected support from Drusilla and Miss Drill. 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, but 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.
Miss Drill is fed up of Miss Hardbroom treating her like one of the pupils and threatens to resign. The Hevvies, however, led by the imperious Miss Pike, are tough and ruthless and during the basketball game, walk all over Cackle's Academy. When they fi This is the first of a two-parter. Miss Drill orders Ethel to take over as Cinderella, and Charlie finds some carrots to use instead of a pumpkin. She escapes to find help but instead, Miss Hardbroom scoops her up and puts her in her handbag.
Mildred becomes concerned that her friends are becoming zombies at the mercy of the computers. Then Mildred discovers a monkey coming from Enid's room. Back at the school, the evil witches have turned Miss Cackle into a frog. She gives Charlie a math test, and as he's failing miserably, Mildred comes to his rescue with a spell. Later at the Head Girl election, on Maud's request, Miss Cackle makes Mildred Head Girl and Jadu Deputy Head Girl in recognition of their efforts in saving the Academy once again.
Mildred's enchantment works on Ruby and Miss Hardbroom and, in the nick of time, Miss Hardbroom saves the day. Von Raffenburg later tells Miss Crotchet of his ambition to find the 'Lost Chord' — a legendary chord which is said to have the power to grant wealth and happiness to anyone who hears it. Meanwhile, the caretaker's nephew, Charlie, visits the academy, but he doesn't believe that the witches are real. A new girl, Enid Nightshade, joins the academy, and Mildred is asked to show her around. No one believes she can manage it. Up until now, Mildred and Ethel have been enemies, but now they must put their differences aside and show that they have all the necessary magic to produce a win from thin air.