69. The Green Death

What started with the Doctor regaining his ability to travel through time and space, ends with one of the best departures in Doctor Who history. The season 10 finales sees the departure of companion Jo Grant, going off to marry a man and go travel the Amazon River. Despite the numerous courtships and proposals Jo has received throughout time and space on her travels with the Doctor, it's a present day Earth man that wins her heart. And they actually develop Jo's relationship with Cliff over the course of the episode. When the story concludes and Jo breaks the news to the Doctor, you actually feel her conflicted emotions and you see the Doctor visibly heartbroken. The Doctor fades away into the background as people toast Jo's engagement and you see his silhouette drove off into the sunset. This marks the beginning of the end for the 3rd Doctor's tenure. With the tragic passing of Roger Delgado and the departure of Katy Manning, the Doctor's little UNIT family is slowly breaking up and you can see the toll on Jon Pertwee's face. While the introduction of Elizabeth Sladen's Sarah Jane Smith next season is a great shot of energy for the show, it's also the slow wind down for Jon Pertwee as the end of the 3rd Doctor approaches,

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