70. The Time Warrior

The Time Warrior kicks off season 11 and Jon Pertwee's final series as the Doctor. After four seasons, Pertwee begins his fifth and final turn in the role, the longest actor to date. The story begins with a new opening title sequence and slightly retooled theme. We are quickly introduced to the amazing Elizabeth Sladen as the best companion ever- Sarah Jane Smith. This is a great introduction story for her and adds some much needed energy to the show. Her relationship with Jon Pertwee's Doctor is very different from his with Jo Grant, but a welcomed change. Knowing her future travels and adventures over the next 40 years, this story so well defines this character and speaks to Liz Sladen's ability to sustain this character for the rest of her life. This story also introduces the Sontarans to the list of great Doctor Who monsters. While they only appeared 4 times in the classic series, they were quickly revived in the new series and have become regular guest stars. This story is also a great return to historical settings While not traditional straight-on historical, it lays a new blue print for future stories with the alien/monster/other antagonist creating havoc in a historical setting. For an eleven year old show, now on it's third lead actor in his fifth year, this story introduces so many new and fresh elements that the show once again feels reborn.

http://en.wikipedia.org/wiki/The_Time_Warrior