You don’t have to have been paying much attention to Dr Who to know that Peter Capaldi has been cast as the next Doctor. If you follow it more closely you’ll know that he’s appeared in Doctor Who before as well as in its spinoff Torchwood.
Now a superfluity of Capaldis is clearly a good problem to have. Nonetheless, it does raise a continuity issue. I’d assumed the writers would deal with this problem by ignoring it. After all, if you watch something like Law and Order you will routinely see the same actor playing different roles.
But according to IO9 they may actually try to explain the same person recurring multiple times:
Here’s another rumor about the filming that was going on in Lanzarote. At the time, the announcement that the Doctor would be returning to the scene of an “old adventure,” people assumed that the “old adventure” in question was “Planet of Fire,” which filmed at the same location.
Now, the theory is that the return might actually be to the “Fires of Pompeii,” which guest-starred Peter Capaldi as Caecilius. This could be true, as Steven Moffat has said that they won’t ignore the fact that Capaldi has been in Doctor Who before. The explanation could go even further, and incorporate Capaldi’s role in Torchwood: Children of Earth as John Frobisher, as Moffat has also said:
I remember Russell told me he had a big old plan as to why there were two Peter Capaldis in the Who universe, one in Pompeii and one in Torchwood.
When I cast Peter, [Russell] got in touch to say how pleased he was, I said ‘Okay, what was your theory and does it still work?’ and he said ‘Yes it does, here it is’…
It’s actually quite neat.
Let’s see if we get to see Peter Capaldi act against himself. Fingers crossed they add in Malcolm Tucker just for funsies. [Unreality TV]
I can only assume the latter idea would go something like this: