Even though it's tasked with introducing a new Doctor, a new companion, new Earth-bound set-up, new monster and new pan-military organisation (the UNIT family, set to for the bedrock of the show over the next six years), Spearhead From Space remains one of the most accessible, engaging and relevant Doctor Who stories over 40 years later.
Actor-turned-director Derek Martinus - who worked on several Doctor Who stories including iconic stories such as Mission to the Unknown, The Tenth Planet, Evil of the Daleks and The Ice Warriors - also directed one of the best Blake's 7 episodes - Trial. Perhaps his most significant contribution, however, is Jon Pertwee's debut serial.
The first story in season seven is so good that it basically provided the template for relaunching the series in 2005 - huge kudos to producer Derrick Sherwin for that - perhaps more interestingly it's where a repeat season began in 1999, where it wiped the floor with the competition at the time. Sadly The Silurians and Genesis of the Daleks couldn't sustain the viewing figures and, though both stories are excellent, it's easy to see why.
Spearhead is one of a very few stories that is sufficiently visually striking and narratively dynamic that you could show it now - with perhaps only some of McCoy's later adventures, some vintage Tom and the odd Davison also passing muster - without a vaguely patronising filter of nostalgia or oddity.
A heavily-edited trailer for Spearhead aired for a week or so beforehand with some noisy, chugging guitar complementing a series of the show's more impressive visuals - crash zooms on Autons, battle scenes, shop-window dummies coming to life and Pertwee being irascible and dramatic. But Spearhead doesn't really need reengineering, thanks to Derek Martinus' electrifying direction.
The difference from The War Games, also excellent but shot largely on video, in monochrome on the BBC's trusty four-camera studio set-up, is astonishing. Spearhead has the incredible good luck of being shot entirely on film, in colour and on location, bringing Doctor Who very much into the real world, albeit a distinctly period idiom and a rather muddy colour palette.
On Bluray (it remains the only classic series story on this format) it looks like it could have been shot ten years ago - thanks in part to the nature of the filming but there's a significant debt to Martinus' editing. Scenes such as the one where an Auton dispatches Ransome in a UNIT tent (detailed above) are a blur of very quick shots - a dozen in 20 seconds framed by two lengthy scenes that bookend it, leading in with a tight shot on Liz worrying about the creature and moving into a scene where Munro reports that the creature escaped the UNIT platoon. It's like a slap around the face and is the most dynamic the series has looked so far and gives the impression of a series not just regenerated but completely overhauled.
Martinus isn't simply a dab hand with editing, however. There are techniques here that we've never seen before and probably don't ever see again - at least in the original series. The real-world setting makes allowance for the kind of shots we might expect to see in modern-day thrillers - shaky hand-held verite-style footage of the The Brigadier under siege from a news pack at the cottage hospital where The Doctor is laid up for instance. It's unthinkable in any other era of the series - classic or new.
The director presents us with footage that might be taken by one of the newsmen, interrupted by journalists jostling for position, a harsh glare from a spotlight shone on Courtney's face. It's totally unlike anything we see on television in this era and another element that moves Spearhead closer to movie territory than a (notionally) children's serial.
Again, it doesn't stop at technical and stylistic jiggery-pokery. Spearhead From Space is dramatically frightening, but it's also eerie. The human-ish faces of the Autons and the facsimiles are right in the depths of the uncanny valley - that space between like and unlike that freaks us out and is where much of the best Doctor Who is based. But it's more than that. The most human face of the Nestenes is Channing, played wonderfully by Hugh Burden. Channing is odd - almost autistically socially awkward - and played as such by Burden; leering, lurking and boggling.
But Martinus heaps it on with a series of shots of the facsimile silently observing people from a distance, visibly processing information; planning. Best of all is the scene where Channing looks through a glass window at The Brigadier who, upon sensing he is being observed, turns around to see Channing's fragmented face slowly gliding backwards out of sight.
We also get a quick cut from a photo of Channing to an unnerving sequence of shots where dolls heads are boiled and decorated in the plastics factory. You could make an argument for this being an extraordinarily subversive scene, heavy with symbolism, but even on a visual level it's peculiar, perhaps unique, in Doctor Who.
Pure mood, pure metaphor, it's hard to see the justification from a narrative point of view; it's there just to reinforce how spooky the facsimiles are - like us, but not - later referenced explicitly in Robots Of Death.
Throughout the serial we do see surprising violence and even gore. A policeman is blasted by an Auton, the Doctor shot with a rifle, the Auton at the Seeley cottage kills a dog (even though the show is too coy to see it offing Mrs Seeley) and the UNIT soldier forced off the road ends up with his face a mass of shattered glass and red-crayon blood. But again, Martinus is more clever than that.
What sells the horror of what's happening is the way people react to what they're seeing: Scobie's horror at opening the doors to his facsimile (sadly missing the dialogue that appears in the book; the facsimile references a previous conversation where Channing promises he will see the dummy soon); Mrs Seeley's horror at encountering the Auton ransacking her home; the terror of the passers-by on Ealing Broadway as the dummies come to life and begin their massacre. We get a huge amount of POV shots here too, just to reinforce the terror of coming face-to face with the faceless.
This being Season Seven, the UNIT crew are professional and believable. Despite remaining relatively anonymous throughout much of the story, Pertwee gets a strong introduction in his debut story, with elements of the irascibility of Hartnell and impishness of Troughton, with enough of his own character breaking through. The Brig, much as he is in the Troughton stories, is very much the professional soldier here - somehow the sight of him issuing orders while wearing sunglasses and dealing capably with a hungry media pack only serve to root him in the real world - and Liz a capable and believablefoil.
It's nice than Carrie John is initially sceptical - and even hostile - towards UNIT and is only won over by the Doctor's charm and intelligence while John Breslin's Jimmy Munro offers us a tantalising glimpse of what could have been. There are no performances that do not work out: the Seeleys, Scobie, Hibbert, Ransome and Henderson all have enough quirks, asides and tics to make them believable. It's another reminder of the importance - seemingly ignored by many Who directors - of casting.
The whole is, perhaps, not quite the sum of its parts. Spearhead, bar one or two efforts from Camfield and Harper, might be the best ever directed Doctor Who story and, like many of the best, benefits from a wonderful confluence of writer, production team, cast and director. Arguably it's a little slight, with a rather dissatisfying conclusion but what makes it so interesting, so impressive, is that it is basically a template for a series that we never saw.
This is true of season seven as a whole, but the visual style of Robert Holmes' story marks it out as unique in the programme's history. The Autons return in the debut story of the next season but it's a very different series - almost comic-book in its garish, overlit visuals and familiar ambiance. Spearhead feels real and because of that it feels more dangerous. It would never feel quite the same again - Martinus never again worked on Doctor Who, there was never another story shot wholly on film again, nor totally on location until Curse of Fenric in 1989, barring the two-part Sonataran Experiment five years later.
As such the story remains a curio in Doctor Who history - a fascinating relic of a Doctor Who that was strangled at birth. Sherwin moved on and the series moves away radically from the nascent template: Season 8 takes a sharp turn away from Spearhead and essentially reboots the series again as cosier, more childish, somehow safer. I'm ambivalent on this - the tone the series adopted was wildly successful and produced numerous quality episodes - but the idea of Doctor Who taking Spearhead From Space as its template is intriguing.
Perhaps because of its unique place in Doctor Who history, perhaps because of Derek Martinus' talent - perhaps a little of both - Spearhead From Space feels unlike any Doctor Who that went before or came since. The director's other stories have much to praise too, but if you want to know what Doctor Who looked like in an alternative universe, look to Spearhead.
• This post began life as a tribute to Derek Martinus, but it said everything I wanted to say about Spearhead for its inclusion in this top 50, so it's been adapted.