Although it sounds like an episode of The Big Bang Theory, it`s actually two glaring continuity errors from part one of the story:
First notice how Peter Davison`s hair changes colour –
So what happened? Probably the shock of realising that Adric is still around. That`s enough to turn anyone`s hair white!
And it`s not just the Doctor Who`s regenerated, his clothing`s getting in on the act too…