This is probably the first time i've ever been excited by a Tv show release.
I'm assuming they will pull a plot arc revolving around the bad guy involved in the latest episode (Something in the WiFi) and opening up the alternative universe where Human Doctor and Rose are living.
English
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The Great Intelligence, that could also work, although it'll likely be a Finale thing not the Anniversary. It is potential enemy as its a Classic enemy since the second Doctor's time. It is a being from before the universe existed.