The most obvious thing to point out about this episode is that it feels like a Hartnell throwback. The continuation directly from the end of the previous serial; the return of the mercury fluid links and malfunctioning TARDIS; the arrival in a mysterious environment, and gradual exploration; the food machine, and the Doctor’s sudden incapacitation at the end of the episode, paving the way for his absence from the second part.

But this in itself is really strange. David Whitaker might have been the show’s first script editor, but he got more ‘written by’ credits for Troughton than Hartnell, between The Power of the Daleks and The Evil of the Daleks shaped the new approach – which usually has the Doctor arrive at the moment of crisis, or even at the instigation of the villain. And in The Enemy of the World he wrote a much pacier, adventurous opening episode than this.

Essentially, the throwback feel can’t be the result of a returning writer unfamiliar with the new house style. It has to be a conscious choice. It feels stripped back. For the first 80% of the episode it’s pretty much just the Doctor and Jamie wandering round an ominously empty spaceship, with only a rapidly-dispatched Servo Robot to provide any kind of obvious threat. When Robert Holmes did the same thing in The Ark in Space, it was a way to establish the new Doctor and companion. But even that’s not the case here. And it can’t even be to cut down on cast costs because suddenly, about 5 minutes before the end of the episode, the action switches to the fully-staffed Wheel.

Which suggests that Whitaker’s script is an exercise in creating atmosphere. Whereas a lot of the horror in Season Five relies on monsters, this goes for isolation and claustrophobia. The eerily empty rocket, drifting aimlessly in space like the Marie Celeste, seems to profoundly disturb the Doctor – who’s doubly vulnerable because he’s just had to disable the TARDIS. He really is trapped. And then, when he bangs his head, becomes incoherent and lapses into unconsciousness, Jamie is left completely alone. In this sense, the lovely scene where the two of them wonder what Victoria might be up to serves to emphasise the loneliness of their own situation.

And it’s only after this point that the focus switches to the Wheel, to reveal that in parallel to this creepy space adventure there’s a base under attack from weird floating egg things – which have come from the rocket. Holding off the reveal until this point makes the episode feel quite different from recent weeks though. It’s deliberately slower, but not empty of incident.

Also quite deliberate is the waddling Servo Robot, the first of several attempts at the tail end of the fifth production block to introduce new mechanical enemies (see also the Quarks and the White Robots) rather than the organic (Yeti – robots but furry, reptilian Ice Warriors, mutant vegetation). After a season’s worth of horror stories, this feels like a pivot towards a more sci-fi style, ready for the arrival of the new space girl companion and in anticipation of the imminent Apollo missions.

Next episode: The Wheel in Space – Episode 2