3.13 - Last of the Time Lords

From IMDB:
Martha Jones secretly returns to England. It's been a year since the Master took over the Earth and launched the invasion. Humans are now a captive race and the Toclafane are building a fleet of rockets they will use to attack other worlds. The Master takes great pleasure in humiliating the Doctor and has Martha's family doing menial chores. Martha has a plan however and all she has to do in get in to see the Master. When she learns of the origin of the Toclafane, she realizes the paradox they have created.

31 out of 33 (93.9%) raters say this story requires a previous story.