After five weeks of build up, this episode could have been a damp squib. The ongoing plot – the Daleks’ hunting of the Doctor – comes to an end in a relatively brief, albeit quite well done, confrontation with the Mechonoids, on film, with some nice cross-fades and Dutch tilts to add some visual interest. The Mechonoids themselves are reasonably well designed, albeit quite unwieldy compared to the Daleks, but they get virtually no screen time and it’s impossible to imagine on the basis of this episode that they could ever have been considered as ’the New Daleks’. It’s actually more interesting to see the Daleks’ range of plunger attachments, here expanded to include some kind of whirling wall cutter.

But while the two mechanical armies annihilate each other, the real confrontations are between the TARDIS crew, and their new friend Steven Taylor – a pilot whose Flight Red 50 crash landed on Mechanus two years earlier during some ill-defined interplanetary war, and has been held ever since as a prisoner of the Mechonoids. Steven is quite fun, although his main characteristics at this point are his understandable garrulousness and his attachment to his panda, HiFi. It’s notable how little work is done to set him up as the new companion compared to the time dedicated to establishing Vicki.

But that’s probably because the real story – the real reason why Mechanus is ‘the planet of decision’ – is Barbara and Ian’s choice to leave the Doctor and get back to London, 1965. To that end, even Vicki is uncharacteristically useless and pathetic during the final desperate escape from the burning Mechonoid city, although she pulls it back a bit when she has to calm a furious Doctor and help him to understand Ian and Barbara’s choice.

Hartnell is even more impressive here than at the end of The Dalek Invasion of Earth. Initially he rages against the notion of using the Dalek timeship. Watch his face as Barbara talks about the chance to go home – his eyes narrow, and his resolve hardens. It’s the one thing he can’t do. He reminds them of how they thrust themselves onto him, and even when Vicki’s persuaded him, he refuses to offer any comfort to them. He even refuses to turn and watch them leave.

After a cute montage – absolutely earned – the joke of arriving back in a London junkyard, and some closure around having to think up a good story for the headmaster, the audience – and the Doctor and Vicki – get to say their last goodbyes via TV. We see that the Doctor’s anger, and his cold walking away from the timeship was a mask for his devastation. He’s used the Space-Time Visualiser to check that they got home safely, and, voice breaking, he finally admits he will miss them.

It’s important that the episode finishes with the Doctor and Vicki, and the TARDIS flying off to new adventures. For the first year Doctor Who was pretty much the story of Ian and Barbara. The second season has been an attempt to reposition the Doctor and Vicki as the main duo – pairing them up, increasing the Doctor’s action heroics at the expense of Ian’s, and making him as much a voice of moral authority as Barbara. At the end of Season One, it’s hard to see how the show could go on without Ian and Barbara. But at this point, even though it’s sad to see them go, the truth is that they are no longer the viewpoint characters they once were. Lambert and Spooner have successfully reformatted the series to make them dispensable in a way they simply weren’t six months earlier.

Next episode: The Watcher