On the first day of the new school year, Maria and Luke arrive in the courtyard, Sarah Jane kissing her new son before she departs, asking him not to caller her “mum”. The two friends then walk into their new school, admiring a new building standing before them.
Watching them from somewhere within the building, the Headmaster of the School (Mr Blakeman) observes them, before focusing his unseen camera on Mr Jeffrey, a science teacher.
Moments later he is leading him through a corridor of the new building, positioning him by a blank wall. Suddenly it rolls back and a giant green arm reaches from within, grabbing Mr Jeffrey.
In the school hall Maria and Luke are met by Clyde, another new student. Somewhat bemused by Luke’s overly formal handshake, he introduces himself as the room falls silent. Mr Blakeman enters, and after breaking wind he rushes through the formalities of ringing in the new school year, Mr Jeffrey joining him on stage part way through.
He explains the new building is the technology block, and some time later he is giving Maria and Luke’s class a guided tour through the building, Clyde noting the strange smell around them, a smell like batteries.
Later, in the canteen, Clyde joins Maria at her table and the two share stories of their parent’s separation. They are shocked by the mouldy food they find on the plates before them, Clyde claiming something weird is going on in the school.
At the end of the day Mr Blakeman and Mr Jeffrey watch the children go before walking off to “test” their new building.
In Bannaman Road, Maria’s father watches as his daughter, Luke and Sarah Jane arrive back from the school in Sarah’s car, and he teases her about not walking home instead. They joke about the issue as Sarah looks on in admiration at their relationship. Once Maria and Luke have gone the two parents talk about the new technology block, Mr Jackson remarking that he helped construct a similar building elsewhere in London; it too had an odd metallic smell within.
Back at the school the two teachers rush about a darkened control room, pulling levers on giant control panels. Electricity buzzes around them and they look around with glee.
In her attic, Sarah talks to Luke about his first day at school, reassuring him that he must take time to adapt to a new life, he may be different but he must live a normal human life. Conversation turns to the new technology block and Sarah reveals she has been investigating it’s construction firm: Coldfire, who have been building identical buildings all around London.
“Makes a change for me” Sarah claims, “Not aliens is it?”
At the school the two teachers continue their work, whilst at Maria’s house her mother arrives to investigate the new house and collect a duvet from her ex-husband.
Meanwhile, the teachers conclude their work and Mr Blakeman claims with relish: “Lights out, London”
Sure enough the lights in Maria’s house all go out. Maria fetches a torch from the cupboard but it too fails to illuminate, apparently from a faulty battery. Across the road the power in Sarah’s attic has gone as well, even Sarah’s specially adapted watch has gone dead.
Maria’s father fetches candles to illuminate the room, but his attempts to light them are of no avail, they die out as soon as he ignites the wick.
In the school the machinery begins to destabilise and Mr Blakeman deactivates it, returning power to the city. The candles light up, the torch turns on and the electricity all comes back to life in Bannerman road.
Mr Jeffrey chides Mr Blakeman for his failure but he is adamant he will manage to correct the fault, one more adjustment and they can destroy the planet…
The next day Sarah leads Luke outside before he starts his walk to school. Sarah reassures him again that he will be okay before moving to talk to Mr Jackson, who shows her the plans to the school he worked in. She finds a blank space on the map, which appears not to have a door.
She arrives at the other school sometime later, whereupon the headmistress explains to her that ever since the new block was installed food has been going off and an odd smell had been lingering in the corridors. Sarah continues to look around; unaware she is being watched via a security camera.
After impressing Mr Jeffrey in his science class, Luke attends Science Club at lunchtime, finding himself and a boy named Carl the only ones in attendance. Mr Jeffrey introduces the circuit diagrams for his and Mr Blakeman’s machine, not explaining its actual purpose. As he hoped, Luke finds the fault in the circuit and writes down a solution.
Sarah makes her way to Coldfire construction, phoning Maria on her way and telling her to investigate the new block to try and find the source of the smell.
At the end of the school day as Mr Blakeman and Mr Jeffrey rejoice at the solution to their problems, Maria, Luke and Clyde begin to scout around, whilst at Coldfire Construction Sarah is greeted by a company secretary.
At the school, Luke realises that the dimensions of the block do not measure up, there is an empty space concealed behind one of the walls.
Sarah interviews the secretary, called Janine, and reveals she has found that Coldfire have been constructing buildings in cities all over the world, and each one has been surrounded by rumours of food going stale and strange smells lingering nearby.
Maria arrives in one of the computer rooms, but Mr Jeffrey is soon on her tail. She hides under a table but he can still smell her presence. He claims that he need no longer hide and proceeds to pull open a zip on his forehead, peeling away his skin to reveal a giant green alien hiding inside.
“I am Slitheen”
Maria flees, whilst at Coldfire construction Janine proceeds to do the same, causing Sarah to flee her office, closely followed by another of the creatures. It follows her into a storage room, where the reporter hides behind a stack of boxes. However, the smell of her perfume is enough to give her away, and the revealed Slitheen advances on her.
At the school, Maria finds Clyde waiting in the corridor, Luke nowhere to be seen. The Slitheen advances on them and they run, whilst Luke manages to locate the entrance to the hidden room, and steps inside. Looking around in amazement he turns to find Mr Blakeman waiting for him.
Cornered below some stairs, Clyde and Maria are found by Carl, who leads them into another room. He closes the door before revealing there is no way out. He reaches up to his forehead and peals away his skin, revealing a far smaller but equally disturbing creature inside.
“I am a child of the Slitheen. And this is my hunt”