A new teacher arrives at Weirdsister, American Dr. Andy Starfinder. A machine that stores up all The Foster's Effect created by the school during the week goes haywire. Mildred, Cas, and Ethel learn that rules are there for a reason.
Monday Morning - Ethel is going on and on about Hobbes in the bedroom. Milly walks out, fed up, to a messy kitchen. During a lecture with Prof. Thunderblast, Milly answers a question wrong - as usual, Ethel gets it right. Hobbes arrives late and answers a question without even seeming to have heard it. He pays her a compliment about her new short red hair. She throws it right back at him, but he cleverly finds a retaliation. The question was about the Bus Spell - all The Foster's Effect backwash from spells is stored up until it is released on Friday. No magic must be done then. Milly is depressed - Cas tells her that new hair won't change anything, "but clothes on the other hand - might be an issue!" They go shopping together. Deirdre and some friends are in the courtyard, making potions. An American (who we find out is called Dr Andy Starfinder) appears, and asks why their Invisibility Potion isn't invisible. He takes some of his invisible Invisibility Potion and walks off. Milly and Cas enter the café - Milly is in her new clothes. The café assistant (called Ben) falls head over heels (literally) in love with her on top of Hobbes and Ethel who are also in the café. Cas tells Milly that Ben obviously likes her - modest Milly doesn't think so. Tim and Azmat turn up - they tell Cas and Milly about Dr Starfinder, the new teacher. Cas makes a joke about worms. The teachers are talking in the staff room - Dr Starfinder is hired.
Wednesday Morning - The first Starfinder lecture, it created a stir with the students. Cas and Milly walk through a wall into the Beetle's office - she's not impressed (although the wall looked a bit fake - it moved when Cas bumped into it!!). Hobbes dumps Ethel - or tells her that they were never going out at all. That's weird - Ethel was going out with Hobbes, but Hobbes wasn't going out with Ethel - how does that work?? Cas, Milly and Ethel do a massive spell to clean up their room, thinking that no Foster's Effect will get at them. Beetle tries to have a word with Starfinder about customs and traditions, but he tells her that it is not her place to tell him anything, so he goes away not knowing about Fridays.
Friday Morning - Ethel, Cas and Milly are getting on really well at the breakfast table. However, they have used magic to produce everything. Deirdre comes in and tells them that what they are doing is dangerous - they obviously weren't listening properly in the lecture then. During Starfinder's lecture, a load of magical backwash starts to be released. Beetle has closed the escape valves to get revenge on Starfinder. Meanwhile, Starfinder is trying to stop the effects with his magical bin, but it explodes. Shakeshaft orders the Beetle to open the valves. She does, and the backwash stops. Starfinder goes to talk to Thunderblast about his bin, leaving the students to clear up the mess.