Although the episode starts with the Doctor Who version of The Ring, we soon see the Doctor has been holing up in a monastery in Cumbria, 1207, meditating on the mystery of Oswald, when his TARDIS phone rings.
If you wondered why the two candidates seemed so chippy the other night, think about how you would feel if you had to confront the younger, more idealistic version of yourself after you sold out all your principles for a shot at the brass ring.