The story that for many years was incorrectly said to be a last minute filler because the sets for Marco Polo weren't ready (not remotely true) has a fuzzy genesis, but it's largely to do with numbers, and the fact that the show itself might well be brought to an end. So this must be on script editor David Whitaker's mind as he writes the story that at one point might have been the very last anyone ever saw of Doctor Who. No guest cast, no new sets ... it's more a can of Is There Enough Information? Well, in true THTT style, your host has had a bash!