school in recent months & replaced most of the staff
with his own people - introduces a journalist from the Times who's come to the school to
write a story about him... a woman named Sarah Jane Smith (Elisabeth Sladen).
The Doctor, caught off guard by the sight of one of his
dearest friends, at first doesn't let on about his identity; instead, he plays along as
the new teacher, sounding Sarah Jane out about her real motivation for coming to the
school. Later that evening, as the Doctor, Mickey and Rose have returned to the school to
do a bit of snooping, Sarah Jane has also broken into the school, and discovers the
presence of the TARDIS. At that moment, she's reunited with the man who abandoned her many
years before, but who she has remained eternally fond of. Mickey, meanwhile, discovers a
closet full of dehydrated rats, while on top of the school, Finch and a bat-like creature
watch the four with eagle eyes. When the Doctor suggests that they analyze the liquid Rose
discovered in the kitchen, Sarah brings him to the boot of her car, where she reveals the
broken-down, but possibly still functional, robot dog, K9 (voice of John Leeson).
While Mickey and Rose remain curious about the Doctor's
relationship with Sarah Jane, the two reminisce about their travelling days together. The
Doctor succeeds in repairing K9, who tells him the goo is Krillitane oil, a nasty
substance belonging to the alien Krillitanes, beings who have evolved by taking on the
characteristics of other species. Somehow, the Krillitanes and their leader, Finch, are
doing something with the oil to the school children, but Finch himself promises the Doctor
that it's not evil, just impressive on a galactic scale. Meanwhile, Rose and Sarah Jane
who have taken an immediate dislike to each other, have words, while Mickey thinks about
his role in the group. He feels he has the same status as K9, the 'metal dog' role always
being on the sidelines.
Later, Finch offers the Doctor the chance to take control
of his destiny after the Doctor discovers the secret about the project the Krillitanes are
brainwashing the children into completing. It seems they're trying to crack the Scasis
Paradigm, the universal theory that controls the building blocks of the universe. With the
theses powers unleashed, the Doctor would be able to recreate the Time Lords and run the
universe. The Doctor decides to pass, which sets the Krillitanes on the loose. With the
aid of a young student who's escaped the Krillitane mind control devices, Mickey crashes
his car into the building to rescue everyone, but the Doctor, Rose and Sarah Jane are
stranded inside the cafeteria...until K9 arrives on the scene, using his rapidly running
out of power laser to ward the Krillitanes off.
The Doctor comes up with a plan to deal with the invading
aliens, while Mickey helps free the children by pulling the plug on the computers. The
Doctor says goodbye to K9 for one more time, before evacuating the building. In the
kitchen, the Krillitanes attack K9, before he's able to stun them by blasting the vat of
oil - exposing them to the viscous goo which has become highly toxic to them - and then
blowing up the entire room, taking himself in the process.
Sarah comes to see the Doctor and Rose off and has made
peace with Rose. They now share a bond as friends of the Doctor, Sarah turns them down on
his offer to join them, but Mickey asks to go as well. He wants to become more than just
the man on the other end of the phone, and instead wants to see the universe. While Rose
and Mickey prepare to leave in the TARDIS, the Doctor says one last goodbye to Sarah Jane
Smith, who is finally able to put the past behind her. The Doctor leaves her a gift: a
fully rebuilt K9 whom she spots as the TARDIS slowly fades out of sight.
