"The day I was born, I saved the world. Now I've helped to destroy it."Luke and Maria start their first day at their new school, but not everything is as it seems, the cafeteria food is mouldy, the air smells like batteries, people are spontaneously getting ill and worst of all, the portly head teacher has gas problems. Aided by their new friend, Clyde Langer, Sarah Jane and the gang discover a sinister revenge plot engineered by the Slitheen, for what the Doctor did to another branch of their family.
— Luke Smith
- Adventure Rebuff: Both Sarah Jane and Maria try to make Clyde go away for his own good. It doesn't work.
- Age Lift: Janine was supposed to be in her twenties in the script, but it seems the production was unable to find an overweight actress in that range, as in the broadcast version she is considerably older. The novelisation uses her originally intended age.
- Bland-Name Product: Clyde's Wolverine brand body spray, a play on the real brand "Lynx".
- Continuity Nod: Slitheen in Downing Street, which happened in "Aliens of London" and "World War Three", and Sarah Jane learned about in "School Reunion".
- Sarah Jane: (remembering) Slitheen in Downing Street.Maria: What?Sarah Jane: Something a friend said once.
- Death of a Child: Implied but not shown; Korst, the young Slitheen, is wearing a twelve-year-old boy disguise that (given what is revealed about Slitheen disguises in their first Doctor Who appearance, and the real Mr Jeffrey is seen meeting a similar fate at the beginning of the story) must have been made by killing and skinning a real twelve-year-old boy.
- Even Evil Has Loved Ones: The Slitheen beg Sarah Jane and the others to let the young Slitheen live.
- Evil Teacher: The Slitheen pose as teachers worldwide during their revenge plot.
- Exposed Extraterrestrials: Slitheen, when not in human suits.
- Fat Bastard: The Slitheen, as usual.
- Foreshadowing: The scene at the end when Clyde asks Mr. Smith where he came from and the computer responds by shocking him foreshadows a revelation in the season finale.
- Hold Your Hippogriffs: "Oh, for the love of Clom!"
- Incest Subtext: Between Glune, the headmaster Slitheen, and Kist, the science teacher Slitheen, which might help explain why the Slitheen are so screwed up.
- Kill and Replace: All of the Slitheens' human disguises, although Jeffrey is the only one seen meeting this fate onscreen. (The novelisation adds a prologue where the real Janine is killed.)
- Large Ham: All of the Slitheen.
- Lost in Transmission: As the Slitheen begin to drain London of power, Mr. Smith informs our heroes that the Slitheen are "notoriously hypersensitive to *fzzt*", and they're left to figure out the end of the sentence from the information they already have.
- Nice Job Breaking It, Hero!: Luke gives the Slitheen the equations they need in response to a transparent ploy that you'd have to have been born yesterday not to see through. Unfortunately for Luke, he was born yesterday.
- The Night That Never Ends: A variation — instead of blotting out the sun, the Slitheen are trying to drain the sun of its energy.
- Parental Bonus: Maria's divorced mother asks her ex-husband if she can have the double bed size duvet as he won't need it having a single bed. Her mannerisms and delivery of this line is enough to make older viewers think she's making fun of his sex life.
- School for Scheming: The Slitheen have set up bases within schools worldwide to power their sun-draining machine.
- Second Episode Introduction: Clyde.
- Shout-Out: "Let's have a High School Musical moment. A group hug will sort everything out."
- Toilet Humor: Luke doesn't understand it.
- Two of Your Earth Minutes: The teacher who's really a disguised Slitheen refers to "your... our main electrical supply".
- The X of Y