Goodbye, Sarah Jane Smith: Part 1

Plot:

Mystery woman Ruby White moves into Bannerman Road and, after an awkward start in which she appears unfriendly,she saves the lives of Sarah Jane and her young friends from an inter-galactic invasion force, revealing that she too is an alien hunter. At the same time Sarah Jane is beginning to feel weak, suffering from memory loss and mindful that she should give up her life fighting space monsters and retire. She duly hands all her knowledge, including control of Mr. Smith,over to Ruby. This proves to be a terrible mistake as Ruby herself is an alien in disguise who ...