32. The Time Warrior (Third Doctor)
The previous serial, The Green Death, said goodbye to longtime companion Jo Grant. The Time Warrior fixes that by bringing us the
greatest companion of all time, Sarah Jane Smith. The story begins in the Middle Ages, where a bloodthirsty warlord is preparing to take a nearby castle. However, an alien known as a Sontaran who has crash-landed offers to give the warlord weapons in exchange for shelter and a place to work. Through sciency ways, the Sontaran is able to teleport scientists from the future (the 1970's) to his castle workshop, where he brainwashes them and gets them to work on making weapons for the warlord and repairing his own ship. The Sontarans would later go on to be among the most famous and frequently appearing foes in Doctor Who, with their most recent appearance in the 2012 Christmas special "The Snowmen" (although as an ally in this case).
31. The Dalek Invasion Of Earth (First Doctor)
Suppose for a moment you're Terry Nation. It's 1964 and the previous year you invented what is now the most popular villains in television. Now you need to write a follow-up to your epic serial that introduced the one, the only, the Daleks. What do you do to ensure this time it equals the first? Easy. Have them invade Earth. The year is 2164, and Daleks have completely overtaken the planet and enslaved the inhabitants. Many are put to work in the deadly mines, some are converted into mindless roboslaves. But there's a small portion of the population that survives, that have escaped the clutches of the Daleks and are forming a rebellion. The Doctor and his three companions join forces with them and set out to erase the Dalek presence on Earth. Cue dramatic music.