|Doctor Who-The Dalek Invasion Of Earth|
Upon the TARDIS arriving in London Ian and Barbara believe they have returned home. After some sleuthing on the part of Ian and the Doctor,it's found that this London is a wasteland in the mid 22'nd century. Earth has been invaded and the few humans left are planning a revolt,with others have been transformed into zombie like Robomen. It isn't long after this that the reason for all this chaos is found: a group of time travelling Daleks have invaded the Earth. It's up to the Doctor,his companions and the few remaining humans to keep the Daleks from bringing down re-enforcements and quell the infestation of the Robomen. In the meantime Susan has become smitten with one of the humans. And while in the end the Doctor successfully stops the Daleks invasion,he deliberately locks Susan out of the TARDIS,to allow her to grow and continue her adult romance with her human companion.
It's this episode that concludes with the first doctors famous "Yes I shall come back" speech to Susan. It's a coming of age story for her character,as she is no longer as clingy to her grandfather and develops another type of relationship on her own. So on that front,again the soulless,aggressive Daleks create a set of circumstances that lead inevitably to Susan's departure. Not only does it allow her to have her independent love interest (the first time the idea of romance was strongly emphasized in the program) but the Dalek's planned conquest of Earth and it's view of the human race as utterly worthless on it's own strengthens that state of independence for Susan. With it's epic scope,compelling camera work and location shooting as well as that whole coming of age concept make this one of the major triumphs of the first doctor era serials.