4. The Path To Redemption
One of the great strengths of Steven Moffat's script is that three incarnations of the Doctor don't just meet; they come together for a game-changing reason. It's time to move the story forward but a single Doctor can't do that because they are only a fragment of a whole. In order for the path to truly be altered, the entire consciousness of the being known as the Doctor, in all his incarnations, including one we haven't seen yet, must work together. The Doctor can no longer hide from parts of himself - not if he wants to save his home. The question of identity is a central theme in "Doctor Who". In fact it's the title of the show. It's a bold move to reveal so much of the Doctor's psyche. It's not so much that he loses his mystery but we certainly know him better now than perhaps we ever have. This crisis of identity is mirrored in the subplot with Unit and the Zygons. The only way to force them to solve their differences is to strip them of identity so that they don't know who they truly are. Only without that bias can they work together to craft an equitable treaty.