Planet of Giants ... Watched the as-aired version. I watched some of the reconstruction of episode 3, but was too tired to keep going. Quite a nice story, though some odd editing choices in that "final" combined episode.
I don't think I was aware of this at first. It was filmed as four episodes. Someone at the BBC decided three and four were too slow, and had those edited together as a single episode. That left a one-episode hole in the schedule that was later filled by the Dalek cutaway leading into Dalek Masterplan.