January, 1970. In the six months since Doctor Who went off the air, the biggest news has been the Apollo 11 and 12 Moon landings. Four human beings have walked on another planet, and looked up to see the Earth in the sky. Which makes the opening shot of this serial – our lonely planet, floating in the blackness of space – especially poignant.

There’s something to be said for the argument that once we got to the moon and found nothing there, space lost its appeal slightly. Certainly, in the popular imagination the early 1970s are more notable for their introspection – meditation and mysticism – than the questing spirit of the 1960s. Having established that we were alone in the Solar System, if not the universe, there was suddenly an increased sense of urgency to protect our own planet. Environmentalism was on the rise, and series such as Doomwatch captured the mood of the times, where the biggest threat to humankind was our own short-sightedness.

On TV, Star Trek‘s voyage to strange new worlds, new life and new civilisations, ended in 1969. The biggest sci-fi movie franchise was the Planet of the Apes series, which, famously, was Earth all along. So ending the Doctor’s adventures in space and time and exiling him to 20^th Century Earth fits very well with the zeitgeist. And as the first story in the new house style, Spearhead from Space is promising.

Given the persistent idea that the UNIT stories take place in the future, it’s interesting that in the first scene of the 1970s, a woman is in charge, giving a male radio operator a dressing down for his fanciful speculation. Blink and you miss it, but it’s an important detail: straight away, the show establishes that we’re in a time when women are the unquestioned equals of men. Later, the Brigadier is shown to be embarrassed by the chauvinist attitudes of a stuffy old British Army general, siding with the smartest person in the room – Dr. Elizabeth Shaw – rather than the most senior man. At this stage, the Brigadier is being set up very much as a ‘new man’, which ties back to The Web of Fear when he’s far more open than his colleagues to the possibility of a Police Box that travels in time and space. Given he’s later reduced to chauvinist comic relief, the Brigadier we get here is much more in the spirit of Haisman and Lincoln’s original creation, and a more interesting character.

Robert Holmes establishes the new set-up of the series with an economical two-hander between the Brigadier and Liz. Reiterating the predominant theme of the Troughton years – space is dangerous and the Earth is surrounded by alien monsters hungry for a piece of us – the Brigadier tries to convince Liz to become UNIT’s new scientific advisor. And fuelling the mood of paranoia and mistrust of politicians, he states, “There was a policy decision not to inform the public” about two previous alien invasion attempts.

So before we even meet the new Doctor, Holmes has established the Brigadier as the leading man in this show. There’s a hint that the new dynamic might be the Brigadier and Liz – who enjoy a slightly flirtatious relationship – being assisted by an eccentric alien Doctor, who’s a whimsical secondary presence, coming up with moments of genius in the lab: a sort of precursor to Dr. Walter Bishop in Fringe. This fits with reports that Derrick Sherwin wanted to cast a known comic actor to play the guitar and goof around. But all that’s put paid to the moment the new Doctor wakes up from his coma.

If Troughton was charismatic, and made the Doctor into the dominant lead of the series, then Pertwee just turns that up to 11. He dominates the screen, from the moment he starts pulling faces into Liz’s mirror. Taking Troughton’s occasional clowning and charm, and Hartnell’s screen-hogging arrogance, Pertwee is a presence in every one of his scenes. It’s impossible not to be drawn to him. Tom Baker, with an uncharacteristic hint of awe, described him as a glittering light bulb, and he was right. Any idea the producers might have had to make Courtney a lead are clearly untenable when Pertwee is so obviously the star of this show. Director Derek Martinus, one of the series’ best, has clearly clocked this, and gives the audience plenty of close ups of the new lead, and enough time to show his flair for comedy, for example in the shower scene. When the new Doctor drives up to UNIT’s secret headquarters and demands to see the Brigadier, you can practically see Derrick Sherwin – who’s playing the hapless security guard – roll over and surrender.

Of course it helps the new Doctor that his predecessor hasn’t been seen for six months, and that the last time we did see him he was at rock bottom, But nonetheless, even without a Ben or Polly to help the audience accept him, Pertwee establishes himself in the role remarkably quickly, and with none of the lingering suspicion that Troughton’s Doctor engendered.

While the audience has been focusing on the Brigadier setting up the new format and Pertwee taking over the show, in the background the Auton invasion has been unfolding quietly but methodically, the pieces dropping into place before things properly kick off in Episode Three. We ought to give Robert Holmes credit for this balancing act, because the big invasion story is really only a sideshow while UNIT and the new Doctor to set themselves up, and then an opportunity for them prove their mettle. However, this is only really problematic when you notice that the second and third cliffhangers involve bit-part actors being threatened because our leads aren’t really yet part of the invasion story.

It’s the fourth episode which gives us the money shot – one of the best of the entire run – when the Autons smash their way out of their window displays and start gunning down shoppers. This is the Yeti on the Loo scenario playing out in a way we’ve never really seen before – the War Machines shooting a man in a phone box are so out of the ordinary that they might as well be Daleks on Westminster Bridge. But this image takes what Doctor Who is good at – juxtaposing things that shouldn’t be together – and pushes it to a new level. This isn’t putting two very different things side by side: it’s putting the bizarre inside the mundane, thus making the everyday horrifying and uncanny. A shop window dummy that’s actually an alien robot is horrific in a way that a mythical abominable snowman that’s actually an alien robot isn’t. The genius of the TARDIS – an alien time machine inside a London police box – appropriated as the way to scare children.

Robert Holmes and Terrance Dicks clearly recognise this is the real innovation of Spearhead from Space, and to their credit when they re-make this story in the following season, the whole thing revolves around everyday objects being possessed by alien intelligence. Which results in Holmes getting his first rap on the knuckles for going too far into the realms of horror. Nevertheless, he clearly takes all the right lessons from this story when he becomes the show’s head writer.

So, this is clearly one of the classics, and it kicks off a highly-acclaimed season. Which might suggest that Derrick Sherwin’s instincts were right, that the show did need to go with the zeitgeist, and bring the Doctor down to Earth. In the short term, the approach works. However, looking at this story critically we have robot monsters collecting alien energy spheres to help manifest a disembodied intelligence. And we have monsters waking up and marching around London, while the Doctor and UNIT go to their factory with a gizmo that disrupts their brains. Yes, it’s a reductionist description, but the reality is there isn’t much here that hasn’t already been done in The Web of Fear or The Invasion. There’s even a dismantled Yeti sphere included in the Doctor’s Nestene-killing gizmo, while the Auton factory is exactly the same location as Tobias Vaughn’s factory. For all that, though, Spearhead from Space is unquestionably a success.

The real problem with the Earth exile format is that after 1970, it goes on for another two years. Once Season Seven has cycled through variations on Quatermass (Inferno tries to break the mould with a premonition story with sci-fi trappings), Season Eight struggles to find anywhere new to go. Hence we get two re-makes of this and another buried evil story. If anything, the miracle of the Pertwee era is that they managed to make a short-term decision, prompted by production problems and mounting costs, spin out so long. While there’s nothing inherently wrong with UNIT stories – after all, series like Doomwatch and UFO managed to get by just fine on a similar premise, and The X-Files ended up lasting for nine years – this in itself is telling. Other shows can do these stories as well as Doctor Who.

All along, the issue is staring us in the face. In the second episode, Liz re-states the basics of the series: “You really believe in a man who’s helped to save the world twice? With the power to transform his physical appearance? An alien who travels through time and space in a Police Box?”. The trouble is, she’s describing a show that’s more interesting than the one they’re making now. In the third episode, the Doctor and the Brigadier spend ages talking about the TARDIS – even though we’re not going to see it for another 15 months. Yes, you can do very good, even great stories about invasions of Earth. Spearhead from Space is one of them. But they’re not the only stories this series ought to be telling.

The Doctor showed us the dawn of man and the end of the world. We saw planets ruled by butterflies, and a land where every story was real. We visited China with Marco Polo and saw the Daleks on top of the Empire State Building. We’ve seen the wonders of the universe because of a madman with a box. But take his box away, and what do you have left?

Next Time: “Outside those doors, we might see anything. We could find new worlds, terrifying monsters. Impossible things…” After two years’ absence, Doctor Who returns in Colony in Space.