Oh, Susan wasn't my idea - she was just one of the many suggestions I saw floating around - and it made some sort of sense (apart from the grandad-snogging) because of the return to Coal Hill School and the setting up of Clara as a new sort of Barbara. And the keys. And I never believed it was River, because she wouldn't say "boyfriend" when she could flaunt "husband".

Of course, when I say "that precise combination of malevolence and obsession with the Doctor (and dancing!) had to be the Master", I suppose I have to allow for "or someone doing their damnedest to impersonate the Master". But I would be quite surprised.