Director: James Hawes
Show Stars: David Tennant (The 10th Doctor (Season 2)), Billie Piper (Rose Tyler)
Recurring Role: Noel Clarke (Mickey)
Guest Stars: Elisabeth Sladen (Sarah Jane Smith) , John Leeson (Voice of K9) , Eugene Washington (Mr. Wagner) , Caroline Berry (Dinner Lady) , Rod Arthur (Mr. Parsons) , Clem Tibber (Milo) , Benjamin Smith (Luke) , Anthony Stewart Head (Mr. Finch) , Heather Cameron (Nina) , Lucinda Dryzek (Melissa) , Joe Pickley (Kenny)
Production Code: NCFS087L
At Deffry Vale High School, Headmaster Finch talks to a child who has been sent to visit the school nurse and has no one at home. Finch takes her into his office and a scream rings out. In a classroom, the Doctor enters and starts teaching Physics. The class is less than enthused except for Kenny, who can answer the Doctor’s questions with remarkable speed.
In the cafeteria, the Doctor gets lunch and meets up with Rose, who is unenthusiastically undercover as a lunch lady. She comes over to the Doctor and they talk quietly about how Mickey set them onto the fact something was going on at the school, and Kenny seems to possess alien intelligence. The head cafeteria worker informs them the menu has been prepared by the headmaster, and Rose should get back to work. As she goes back to work, another teacher, Mr. Walker, takes a student out of the cafeteria.
Rose calls Mickey from the cafeteria and he gives her a heads up that there’s been an increase in UFO activity in the area. In return she tells him that the staff were recently replaced. She notices one worker has some oil in a vat spilled on her and is rushed for treatment. The head lunch lady sees Rose and denies anything is wrong.
In a darkened room, Mr. Walker hooks some students up to computers via headphones and puts them through some kind of exercise which they all robotically respond to. Finch is escorting a reporter, Miss Smith around, and she’s impressed he’s turned the place around. He insists she eat the chips.
The Doctor is talking to a teacher who also mentions how Finch is relatively new and the rest of the staff are new except for the Doctor. Finch comes in and introduces the reporter as Sarah Jane Smith. The Doctor recognizes her and introduces himself as John Smith. They talk about how children are getting ill and he encourages her to check out the situation.
Out in the hall, another student Kenny wanders into the testing room with the computers. He spots a bat like creature underneath the table but as it stands up it becomes Walker, who tells him to get out. Later Sarah Jane sneaks into the school while the Doctor, Mickey, and Rose are also roaming the hallways. The Doctor goes to check out Finch’s office while Mickey and Rose go to get a sample of the oil. Sarah Jane hears strange noises and goes to check them out, while Rose sees a strange shadowy figure lurking overhead. Sarah Jane goes into a basement room and finds the TARDIS, which she recognizes. She backs out of the room and bumps into the Doctor, who introduces himself as the Doctor. They compare notes and it’s clear they’re there for the same reason. Sarah Jane is then upset, believing he had died when he didn’t come for her. They’re interrupted by Mickey screaming and Rose comes by. The Doctor quickly introduces them.
They go on to find Mickey, who screamed upon finding vacuum-packed rats. It becomes clear that Sarah Jane and Rose have issues with each other. They check out Finch’s office and find that a group of alien bat like creatures are hanging from the ceiling, asleep. They run out as one of the creatures wake up.
Outside, Sarah Jane shows them K-9 in the boot of her car. They go back to a restaurant while one of the alien creatures flies overhead, and Finch calls it down to see what it saw. Sarah Jane and the Doctor talk while he works on K-9. Sarah Jane expresses her regrets of how she had to return to “normal life” on Earth, and how he didn’t come back. The Doctor gets K-9 working and it analyzes the oil and determines that it originates with a race known as the Krillitanes, which adopt the physical properties of the race they conquer.
Rose confronts the Doctor on the fact he never mentioned Sarah Jane to her, and in return he talks about how he never ages but humans decay, and he’ll outlive them all. He mentions that he’s a Time Lord and Finch and his accompanying creature overhear. The other one flies by without touching them, much to the group’s confusion.
The next day at the school, the Doctor sends Rose and Sarah Jane to check out the computers while he goes to confront Finch. They face off against each other by the pool, and Finch introduces himself as “Brother Lasser,” and tells of how they use a morphic illusion to conceal their real appearance. Finch knows about the Time Lords and how they’re extinct, and dares the Doctor to figure out his plan. The Doctor warns that he no longer has much mercy and gives Finch one warning. In return, Finch warns that he’ll join with him the next time they meet.
While Mickey sulks in the car with K-9 while watching the place, Rose and Sarah Jane work on the computers. Sarah Jane tries to warn Rose that things may be different for her once the Doctor leaves her behind. They soon start to bond over their shared experiences and the Doctor returns to find them laughing.
Finch tells his fellow aliens to seal down the school as they must initiate the “Final Phase.” All the students are called in to their rooms and the staff to their staff room. Kenny is leery of the summons but the rest of the children go inside. Rose redirects the children coming into their computer room while Finch and his aliens confront the rest of the teachers and announce they’re having an “early lunch” as screams break out. Other children are escorted into their rooms as Kenny looks on.
Walker hooks up the students to the computers where they begin processing information, while the Doctor determines what the program is. Kenny runs through the school halls and sees all the students at work on the computers. He runs for the doors but can’t get out, although Mickey sees him pounding on the glass. Mickey gets K-9 active and it suggests they drive through the glass.
The Doctor realizes that the Krillitanes are trying to solve Skasis Paradigm, which will give them access to the building blocks of life, matter, and energy. The oil accelerates the children’s intelligence, giving them the necessary mind power to run the computation. But the process is stealing the souls and the imaginations of the children they use. Finch arrives to suggest that if the Paradigm is used for good, it can be a great gift. He suggests the Doctor use the Paradigm at his side and bring order to the universe, as well as preserve the lives of his companions. Although the Doctor appears tempted, Sarah Jane points out that all things must die at their proper time, and the Doctor hurls a chair at one of the computers. Mickey and K-9 burst in as Finch cries out for his fellows, which revert to their true forms. They run through the cafeteria and meet Kenny, where the Krillitanes confront them and attack. K-9 drives off the attackers and the others take refuge in a locked room.
The Doctor realizes the Krillitanes can’t handle the oil they use, so they head for the kitchen as the aliens burst through the door. The Doctor has Kenny set off the alarm, which overwhelms the Krillitanes so they can escape. Finch cuts the wires to the alarm while Mickey tries to unplug the students and finally pulls the plug, freeing them.
Finch and his staff revert to human form while the Doctor sets up the vat for the K-9 to shoot it. However, it will drain all of the robot dog’s energy, “killing” it. The Doctor says his goodbyes and they run out with the Doctor sealing the door behind him. Finch confronts K-9, which shoots the vat and splatters the oil all over the Krillitanes. As Finch confronts K-9, it blows up. Outside, the students celebrate the school being blown up.
Later Sarah Jane goes to the Doctor and he shows off his new TARDIS interior. He suggests she come along but she says she can’t do it any more and needs to find a life of her own without waiting for the Doctor. Mickey asks if he can come with the Doctor and Rose so he can see what’s out there. With a little prodding from Sarah Jane, the Doctor agrees although Rose is less then enthused. Before leaving, Sarah Jane tells Rose she’ll be there for her when she needs her.
Outside, the Doctor and Sarah Jane say their goodbyes privately and the Doctor says a full goodbye to her. He goes in the TARDIS and leaves, but as Sarah Jane walks off she realizes the Doctor has let something for her--a rebuilt K-9. Together they head for home.