A lot of this feels like it was written for Pertwee, particularly the Doctor’s first encounter with the revived Commander Noah which includes the very third Doctor line, ‘My dear man, if you think for one moment we’re laying claim to Earth, you couldn’t be more mistaken.’ Obviously after half a decade it’s hard for even a writer as witty as Robert Holmes to immediately divorce the character from the actor, or to predict the cadence of Tom Baker’s speech. Equally, at this early stage Baker isn’t redlining chunks of the script or proprietorially declaring he knows the Doctor better than anyone (or being indulged in that). This is one of the interesting things about Baker’s first and final seasons, both coinciding with a new production team under the guidance of Barry Letts, they feel more transitionary than any others in the classic run.

That said, we get a couple of early moments of classic Baker comedy: the first when he comes round, mid sentence, from being stunned: ‘I might have been saying something important. I was saying something important!’ And later when Noah holds him, Sarah and Harry at gunpoint and orders them back to the cryogenic section, and the Doctor, apparently oblivious to the threat, leads the way: ‘You’re absolutely right. There’s no time to lose. Come on.’

Elsewhere, Holmes’ talent for world building gives this a beguiling scope beyond the more straightforward space scripts of Terry Nation or Brian Hayles. Even after they’ve been defrosted, the Ark’s humans are a cold bunch, viewing the Doctor and his friends as if pompous Brits meeting their unsophisticated colonials and either condescending to them (Vira talks to Harry as if he’s a child, and tells him, ‘Your colony speech has no meaning’), or, in Noah’s case, treating them with distaste bordering on disgust. They find the nickname “Noah” an amusement (his real name, Lazar, is equally “amusing”) and speak in stunted euphemisms like ‘condign action’. But there are still flashes of humanity, of the horror these people must have endured to drive them to entomb themselves like Cybermen: ‘There was not much joke in the last days,’ says Vira with an audible shiver, and suddenly they seem a lot more sympathetic.

The monsters they are up against, meanwhile, remain unknowable, voiceless things, despite us having seen one of their corpses, and witnessed something hideous squirming in the solar stacks. The Quatermass overtones are as strong as in Season Seven: Noah wrestling with his hideously transforming hand, the idea that the alien menace that is consuming him has already consumed everything that made Technician Dune, is pure Quatermass Xperiment. The moment when Noah declares, ‘I’m Dune’ is probably the single most horrible moment in Doctor Who since the switch to colour.

Next episode: The Ark in Space – Part Three