One of the major unanswered questions from Series 8 not directly tying to the Nethersphere is the identity of Gus, the computer program who forces the Doctor and the other scientists to study the titular monster from Mummy On The Orient Express. Who programmed him and the general motives behind that episode haven't been given much thought since, but desperately need solving. A promo image for the finale sees Seb looking through a window that looks suspiciously like the shape of Gus' monocle. It could, of course, be a coincidence, but with the Doctor making a point about the mystery being left hanging that seems unlikely. Most interestingly, he has the Doctor's phone number, which ties him into the woman in the shop and, potentially Missy, making the whole plot more important in the grand scheme of things. Conclusion: Gus is, in some way, controlled by the gang at the Promised Land, with the Mummy potentially serving as another test for the Doctor and Clara. And on the subject of their interference with seemingly stand-alone stories...
