4. Clone Saga
Doctor Who is a science fiction story and what is more sci-fi than cloning. Maybe Oswin is a clone of Clara. If this is true, why was Clara cloned? We know that Oswin is a genius. Perhaps Clara is so smart that she was cloned so that her knowledge could be in multiple places at once. Plus, we have seen cloning in Doctor Who before in The Doctor's Daughter. And cloning doesn't have to be genetic. Remember the Flesh from last season?