Re: The Impossible Girl: Who IS Clara Oswin Oswald?!?
Recently I've come to suspect that Clara's mystery has to do with the anniversary date, since the last two seasons have revolved around a date I think that the case this time as well.
As for what Moffat should know, the Christmas special has been planned so he has to have some kowledge of events up to that point.
The greatest science fiction series of all time is
Doctor Who! And I'll take you all on, one-by-one
or all in a bunch to back it up!"
--- Harlan Ellison, from his introduction
to the PINNACLE series of Doctor Who books