The Doctor, Susan and her two school teachers

It all began when the Doctor stole a type TT40 Time Travelling Machine from his home planet of Gallifrey.
It could take on any appearance to blend into its surroundings.
However, the Chameleon circuit, that powered the ability to change appearance was stuck in the 1960's, and so the TARDIS looked like an old police box from the planet earth.
The Doctor had heard stories about Earth from his teacher and he wanted to pass on some of the things he had learned to his granddaughter Susan.
The Time Lords had isolated themselves behind a **** field which covered their entire world.
They were a proud race, once existing only for the purposes of war.
These days however, they were a "bunch of pompous senators".
The Doctor knew there was much more to the universe and he wanted to share it with his Granddaughter. Thus began his legendary journeys.
When he first arrived on earth he sent Susan to a school so she could get to know a few humans.
This worked out well until she bought two of her teachers home, to the TARDIS.
Ian and Barbara, Susan's teachers were intrigued by the oddity of Susan, and wanted to know more about her.
After all, what child thinks that England runs on the Decimal currency system?

Thus, they followed her back to the TARDIS, where they met the Doctor for the first time.