Doctor Who: The Newbies Guide
City of Death
This is the second story in Season 17.
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. In The Armageddon Factor, the Doctor fitted a Randomiser to the TARDIS in order to stop a cosmic entity called the Black Guardian from finding him.
Romanadvoratrelundar (or Romana for short) is a Time Lady. In The Ribos Operation, the White Guardian transported her onto the Doctor's TARDIS to help him in his quest for the Key to Time. In Destiny of the Daleks she regenerated into a new form. This version of Romana is fun-loving and definitely on a par with the Doctor.
K9 Mark 2 is a robotic dog built by the Doctor. In The Invasion of Time, the Doctor left the original K9 on Gallifrey. K9 is very literal in his thinking and is programmed to obey his master and mistress.
Recurring and Historical Characters
Whilst he does not actually appear, this story sees the Doctor visit the studio of Leonardo da Vinci. Da Vinci was perhaps the best example of a "Renaissance Man" - somebody familiar with the entirety of human knowledge at the time. He is most famous for his painting the Mona Lisa. His other work includes diagrams for a number of machines that were ahead of his time - most famously including a helicopter.