Doctor Who: The Newbies Guide
The Seeds of Doom
This is the sixth and final story in Season 13.
The Fourth Doctor dresses in a rather bohemian outfit, notable for its long scarf. He is somewhat alien, willing to play the fool, and almost never gets on with authority figures.
Sarah Jane Smith is a journalist who, in The Time Warrior, sneaked into UNIT in search of a story and ended up accompanying the third Doctor on a trip to the middle ages. Sarah has subsequently become the Doctor's travelling companion.
Recurring and Historical Characters
The United Nations Intelligence Taskforce (UNIT) is an organisation devoted to protecting Earth from extra-terrestrial threats, In The Invasion, the second Doctor teamed up with them to prevent an invasion by the Cybermen. In Spearhead from Space, the third Doctor became their scientific advisor. The fourth Doctor fulfilled that role in Robot before taking off in the TARDIS, and again when called back to Earth in Terror of the Zygons.