Looking at it now, The Tenth Planet is an important story in terms of Doctor Who history. Not only does it mark the first appearance of the Cybermen, it also gives us our first regeneration, a plot device that is still going strong today and ensures that our favourite show survives.
At it's heart, it is a story about a man who is fading into death but chooses his final moments to confront men who have turned themselves into grotesque monsters as a way to stop himself from 'fading' into his death. There is a long stint where neither the Doctor or the Cybermen appear and the story quickly becomes a thriller about the madness of using a weapon that will most likely kill you too. But the Doctor quickly shows up again, followed by the Cybermen for the final showdown. From the first scene in the TARDIS, with Polly giving the Doctor the same clothes he wore in An Unearthly Child, you know this is going to be it, Hartnell's final appearance as the First Doctor and all the way through the story, the way he choses the Doctor to act tells us he knows that he is close to regeneration.
The story neatly sets up how the show was going to be run for the majority of the sixties, a remote base where the Doctor and his companions arrive, followed quickly by the monsters who are determined to invade. Not only does this story see our leading man bow out but it foreshadows how the Second Doctor era of the show was going to look like, much in the same vain as The Invasion, showed us what the Third Doctor era was going to look like. This is our first base under siege story.
But why did the BBC decide it was time for William Hartnell to move on? Well, Hartnell was increasingly ill, he suffered from arteriosclerosis and memory problems that made it hard for him to remember his lines and to handle the physical demands of the job and this was making it increasingly difficult for anyone to work with him as he could get incredibly difficult.
Also, their ratings were slipping and because of this the show would have to change if it were to survive at least the rest of the sixties, let along the next 50 odd years. How does one replace an actor that has become impossible to replace? Well, Gerry Davis came up with the idea that since the Doctor wasn't human, he could be able to change his face and thus, the concept of regeneration was born. But, had this element and Patrick Troughton not one over the viewing audience then it is likely that Doctor Who would have died in the sixties.
The Tenth Planet is another story that has only been partially recovered because of the BBC wiping the most part of their archives. Recently episode 4 has been animated an released when the DVD of the story came out to allow us to enjoy it in full. It is one of the few stories we have with companions Ben and Polly, both of whom joined two stories earlier in The War Machines. Unlike the First Doctor's first companions, Ian and Barbara, as well as Susan who didn't fully trust him, Ben and Polly follow his lead though it becomes obvious to them that he is keeping secrets from them, including what the tenth planet actually is and his declining health.
That strange new object turns out to be the planet Mondas, Earth's twin planet whose inhabitants were once like the human race. However, the people of Mondas found themselves dying and quickly had to come up with a way of saving themselves and turned into the Cybermen.
The Cybermen might look a little different here if you are only used to either the later Cybermen from the classic series or the modern look they were given in the new series. Here they still resemble human beings just with robotic appendages. It is in this story that are perhaps more plausible as what the human race might become. Their cloth faces resemble that of burn victims and how they have enhanced themselves isn't too far from what we can do today. They are more plausible here than later in their stompy robotic appearance. If we were to create Cybermen in real life, I have no doubt that they would look more like the ones here than in the later stories. Their voices are also different but no less chilling and they even have names! This just makes them more of a credible threat as they really do resemble physically and in their social structure the human race they have come to conquer.
Like a planet sized vampire, they plan to suck the earth dry, taking all its energy into their own planet so that can once more live normally. And like a vampire, the Doctor deals with them as so. Stalling them until dawn because Mondas will soon destroy itself. Although Mondas sucking the Earth dry is a threat that is underlined in the story, the Earth would have been in more danger had the Cybermen acted sooner. Any delay would have halted them and it seems, on reflection, all the Doctor has to do is show up.
What is even stranger still is that at the end of The Smugglers which leads directly into this story, the Doctor has no idea why they have landed in the South Pole however, as events unfold, the Doctor knows exactly what is going on. He even gives a chuckle when he tells Cutler there are going to be visitors from Mondas. Indeed, the Doctor gives every indication that he has come to the base to distrupt the Cybermen invasion and as a result, save the Earth.
It is the last heroic act this incarnation of the Doctor does as the next time we see him he is lying on the floor regenerating. The whole regeneration affair is a quiet and intimate one, his 'death' surrounded by his friends. One is taken back to what he say's to Ben moments earlier. "It's far from being all over," and in that moment you know what he means, the show must go on.
And, like William Hartnell believed, the show has been a hit for the past 53 years and is still going strong. And it is all thanks to Mr. Hartnell the man was in those early years, The Doctor.