4. The Tenth Planet - Episode 4
Like The Web of Fear, only one episode is missing from this story. However, it's also a rather crucial episode. Part 4 of The Tenth Planet isn't just the final episode of the Cybermen's first appearance. It's also the final episode of the entire Hartnell era.
After almost 3 years, William Hartnell had certainly left his mark as the First Doctor. Indeed, until the very ending of this serial, he had been the only Doctor. While Peter Cushing had played Dr. Who in big-screen remakes of the first two Dalek stories, it was accepted that those films were in a separate continuity to the TV series.
The idea of someone taking over from Hartnell in the TV series itself - one that was radically different in terms of appearance and performance, at least - must have been difficult, if not impossiblle for the audience to consider at the time.
So it's a shame that Hartnell's final performance in the role is missing from the BBC Archive. While he had been battling health issues - to the extent that the First Doctor had to be written out of episode 3 - he still managed to give one final performance. One that includes a truly iconic line:
"It's far from being all over!"The First Doctor (William Hartnell)
There is one reason why this episode isn't higher in this list - the fact that the first regeneration itself still survives. While most of the surviving footage from the episode is extremely low quality, the regeneration itself still exists and still looks great. The episode itself might be missing, but one of the most important moments in Doctor Who history thankfully still survives.