This one is causing some confusion for me. It's obviously some very complex twist and isn't necessarily very hard to spot, whilst also leaving some nice big options open for TPTB.
Imagine seeing last year's Children in Need special from the viewpoint of the Fifth Doctor (i.e. Peter Davison) rather than, as perhaps we all were, the Tenth (DT)... what would it have looked like? Now, I suspect, we might be seeing a similar story from the Tenth, rather than the Nth (David Morrissey). [PS. "Worked this out for myself" before following up the research for the weblink below which had come to the some conclusion some time ago. Doh!]
Two things:
a) it's Victorian, it's got David Morrissey in a nattily dressed (Doctor Whovian, almost?) outfit, it's Dervla Kirwan, it's got cybermen... and we're going to see two minutes of it during this year's Children in Need (presumably in lieu of a bespoke episodette, due to DT's luvvie commitment for the Bard).
b) David Morrissey has been touted before as a possibly replacement, due to references in RTD's book (discussed on the
Wiki page for "Possible Doctors") but, as per that page, it's possible he's just a future (rather than necessarily The Eleventh) Doctor.
