Doctor Who: The Newbies Guide
The Armageddon Factor
This is the sixth and final story in Season 16.
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.
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. She has more book smarts but less practical experience than 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
The White Guardian is a cosmic entity. In The Ribos Operation he sent the Doctor and Romana on a quest to find the pieces of the Key to Time, which - once assembled - would allow him to restore the cosmic balance .
The Black Guardian is a cosmic entity, being the equal and opposite to the White Guardian. He also desires the Key to Time.
In The Ribos Operation a cosmic entity known as the White Guardian gave the Doctor the mission of collecting the pieces to the Key to TIme in order to restore the cosmic balance. The pieces are disguised as different things scattered throughout space and time. At the very start of The Stones of Blood Romana discovered who was actually behind their mission.
In each of the previous stories in this season the Doctor and Romana successfully found a piece of the Key to Time and are now one piece short of their goal.