The Doctor is back, but for barely more than a cameo – McCoy got nearly as much to do at the start of the TV Movie. Most of the heavy lifting again falls to Michael Craze, who gets by far the best material in the episode, carrying most of the action and proving as useful a second lead as Peter Purves did. Ben is shown to be clever, resourceful and brave, inferring the Cybermen’s fear of radiation, and hectoring the dithering science staff of Snowcap into making a stand on behalf of the planet Earth. He literally saves the world from being exploded by the Z-Bomb and even gets to say, ‘While there’s life there’s still hope’ which is a better epitaph than the Doctor is going to get.

By comparison, Polly and the Doctor are nearly superfluous. The Doctor’s one active contribution is to eavesdrop on the Cybermen’s Plan B, and announce it to everyone, buying a few minutes for Ben and Barclay to come up with their own solution. After that, he passes out again, before staggering back to the TARDIS to regenerate with the parting shot, ‘Keep warm’. Given how momentous the episode is in retrospect, it’s incredibly low-key in light of regenerations to come. The Doctor doesn’t get to make a final, grand statement. There’s no Bell of Doom moment of reflection. He doesn’t even make a conscious decision to sacrifice himself for a greater cause.

The scene itself – from the surviving off-air recordings and Blue Peter clip – looks strange and disconcerting – although the notion of something weird and worrying befalling the Doctor at the end of an episode isn’t a new one (he goes invisible at the end of The Bomb and collapses in pain at the end of The Final Test). This, though, must have seemed different at the time: even if you’d ignored the news of Troughton’s casting, there is foreshadowing earlier in the episode as the Doctor explains his collapse:

THE DOCTOR: It comes from an outside influence. Unless, this old body of mine is wearing a bit thin.

Then there’s his behaviour after the Cybermen have been defeated. he’s started to make a habit of making a quick getaway at the end of each serial, but the Doctor’s desperate need to get back to the TARDIS, and the Ship’s unusual behaviour – flickering lights, switches moving themselves – when he gets there, is something new.

The Tenth Planet is not a great last bow for Hartnell – the Doctor is too sidelined, and the script offers too few opportunities for the Doctor to be “terrible on the rebound”, which often provides his greatest moments (like the showdowns in The Keys of Marinus, The Rescue and The Smugglers). As with the fate of Mondas itself, too much time is spent in anticipation of the explosion at the expense of anything much happening. And yet, knowing that John Wiles planned to write Hartnell out offscreen – literally invisible and mute – and given that they’d never tried anything quite like this before, this is still much better than what could’ve been.

The Ten O’Clock News approach to this story – telling us what is going to happen, then watching it happen, then telling us what happened – robs the Cybermen’s fate of much drama. Rather than a race against time to save the Earth, instead it’s a waiting game for Mondas to disintegrate: ‘All we’ve go to do is sit tight and wait until Mondas breaks up like the Doctor said.’ The Cybermen aren’t as impressive as in Episode 2 either – mewling pitifully as they’re affected by radioactive fuel rods, gunned down, and disintegrating along with their planet. Their story ends, like their planet, falling to bits, rather than with a spectacular bang.

Of all the missing episodes, The Tenth Planet – Episode 4 is the most keenly felt. But having reached this point on the Pilgrimage, I’d much rather have The Smugglers – Episode 4, which at least makes Hartnell central to the resolution. Apparently, in the 1990s when The War Machines was repeated, the regeneration scene was tacked on to the end to show the changeover from Hartnell to Troughton. The fact that that works at all says a lot.

Next episode: The Power of the Daleks