It’s interesting that the opening minutes of this episode play with audience expectations by implying that the TARDIS crew are about to meet the abominable snowmen. Clearly there’s the footprint, which is based on Eric Shipton’s famous photos from the 1951 Himalayas expedition, and then Barbara encounters something hairy and scary that vanishes off into the mountains when she sees it. Given the 1950s interest in yeti, which sparked a Daily Mail-sponsored expedition, a Nigel Kneale BBC serial and a Hammer film, I’m sure a contemporary audience might have been expecting this to go down the route of another ‘monster’ episode. So, when the yeti turns out to be Tegana, it might have been a bit of a let down.

Instead, the script is the first time the Doctor encounters a historical personage. Marco Polo is set up as a rational man who’s willing to believe the evidence of his own eyes, and has a healthy pragmatism that works initially in the time travellers’ favour, when he saves them from freezing to death on the mountain, and then to their disadvantage when he decides the gift of a ‘flying caravan’ is exactly what he needs to win his freedom from Kublai Khan. In a sense, he’s just a thirteenth century version of Za: the TARDIS crew have fallen into his power, and he intends to use them to strengthen his position in the Khan’s ‘tribe’. The flying caravan is his ‘fire’.

Which makes Tegana a malevolent Kal character, irrational and superstitious, resentful of Marco, and accusing the TARDIS crew of being ‘evil spirits’. The cavemen episodes are more of a template than I remembered. Though Marco is much more civilised, and the tents of Lop are more comfortable than the cave of skulls, the time travellers are just as much prisoners at the end of the episode.

As this is the first time the TARDIS has arrived in a historical (as opposed to prehistoric) setting, Barbara gets her first opportunity to show off her historical knowledge, while Ian gets to be a scientist, deducing the nature of the ‘giant’ footprint and explaining the effects of thin air to Marco. Susan is paired up with Ping-Cho, which gives her a first chance to relate to someone her own age. The Doctor is very harassed, which is understandable given he hasn’t had a moment’s rest since they left Skaro. That’s not reflected in Hartnell’s performance though: he’s much more on top of his lines this week. His hysterical laughter when Marco reveals his plans for the TARDIS makes him the third of the crew (after Susan and Ian) to laugh madly in the face of danger. There’s also a slight link between Marco and the Doctor: both are cut off from their own homes, hoping, one day, to get back, although nothing much is made of this in this episode.

The TARDIS has failed in every set of episodes so far, from The Cave of Skulls when it didn’t change appearance; The Dead Planet where the radiation meter didn’t work properly, and The Edge of Destruction when a switch broke. Now ‘everything’s gone to pot’ according to the Doctor: while in future, the Ship’s unreliability is an ongoing motif, in these first episodes it’s a life and death problem, and I think it’s one that’s probably a David Whitaker invention (once he leaves, things like the lock getting cut out or the scanner breaking down get much less common).

The set designs and oriental-themed music are great, and there’s a fun callback to An Unearthly Child when Tegana observes that the TARDIS doesn’t run along on wheels. The cliffhanger is also strong: establishing Tegana isn’t just a threat because he’s superstitious, but also because he’s plotting against Marco and the Khan.

The Roof of the World no longer exists. Not in any of its regenerations. This review is courtesy of the excellent Loose Cannon reconstruction

Next episode: The Singing Sands