Along with The Time Warrior, this is the first Doctor Who story I ever owned on video. I’ve seen it more than any other Tom Baker serial. I’m still surprised by the cliffhangers (my VHS copy having been edited into a TV movie) It feels as comfortable to me as The Five Doctors, which seems bizarre given how uncomfortably strange this is in context.

When I reviewed Colony in Space, the first traditional story made in colour, I suggested Terrance Dicks and Malcolm Hulke had rewatched An Unearthly Child to remind themselves of the show’s roots. The Ark in Space even more explicitly evokes the style of early Hartnell – unsurprising, given that it started as a script by Season One’s John Lucarotti before being rewritten by Robert Holmes. Like The Sensorites or The Space Museum, this almost exclusively focuses on the TARDIS crew exploring a mysterious environment, endangered by trapdoors and defence mechanisms that, with slight adaptation, would be as appropriate to an Aztec tomb or gothic castle as a 30th Century space station.

‘This is a sterile area, keep out!’ barks an automated voice at one point – it might as well be describing the entire space station as the cryogenic chambers. Everything is suddenly dangerous. The universe of wonders Pertwee often described in his “moments of charm” has reverted to a more primal universe of terrors, where everything is potentially lethal. Within the first 25 minutes the travellers are almost suffocated, electrocuted, frozen for 3,000 years and menaced by giant insects. Sarah is teleported into a coffinlike booth where she is forced to endure her own eulogy, accompanied by funeral music. The Poe gothic overtones are obvious: “we have put her living in the tomb” indeed. Worse, the entire human race appears to have encountered an existential catastrophe, only a few hundred remain suspended, like corpses, surrounded by the last treasures of Planet Earth and this last hope now threatened by something entirely alien. The premise is as disturbing as anything we’ve ever seen in the show.

And there is none of the cosiness or reassurance of the UNIT Fam or Pertwee to alleviate it. Harry Sullivan and Sarah Jane Smith have been whisked into time and space by a man they barely know. The third Doctor could be snippy; the fourth is as cantankerous as Hartnell. He curtly dismisses Sarah, ‘In a minute!’, when he’s more interested in his own exploration than hers. He seems to actively resent Harry, calling him a ‘clumsy, ham-fisted idiot’, until Harry starts to make some sensible deductions. Tom Baker’s performance is captivating, from his deadly serious attempts to rescue Sarah (‘Yellow, black, gleen’) to his fulsome praise of humanity, but it’s in no way comforting, there’s no chance he’ll sweep his cape around Sarah to protect her from the monsters. His performance helps make this seem like a suddenly darker and more dangerous show.

Next episode: The Ark in Space – Part Two