The only surviving episode of the story suggests that the whole thing was impressively done. For a start, the location filming – which is extensive – looks great (even if it looks more like the Death Zone than the Himalayas), and convincingly remote. Fair enough, the mix between the daylight location film and the apparent night-time of the monastery during the Yeti attack is jarring, but this is the only moment when the location and studio scenes overlap.

Detsen Monastery is also very convincing, with some good-sized and varied sets giving the place a sense of scale and reality. It’s a little sparsely populated, but in a way that helps as it adds to the idea that it’s a tranquil, isolated place where most of the monks spend their days in quiet contemplation, and where the peace has been disrupted by the arrival of the excitable Travers, the unusually violent Yeti, and the Doctor. Clearly nowadays the number of white British actors posing as Tibetans wouldn’t wash, and casting the Sri Lankan David Spenser (who I discover was the partner of Victor Pemberton) as one because he’s a bit exotic is equally problematic. However, in its favour the dodgiest character of all is the British Travers, willing to throw the Doctor to the wolves if it protects his own quest for fame.

There’s clearly something strange at work because the Abbot is under the influence of an unseen figure whose voice jumps from a soothing murmur to a rasping hiss, and speaks of ‘the powers that guide us’. But the story is taking its time in laying out exactly what is going on – which is a welcome change of pace from those Season Four episodes that gave us all the relevant information up front and then spent a month restating it.

The Yeti themselves are obviously linked to this disturbance – we’re told they were timid, retiring creatures, yet all the evidence we see here suggests they’re very angry indeed. The design continues to be effective when they’re still, or attacking at close quarters – the huge, shaggy heads and massive limbs really convey their power and size, and the Yeti that crawls its way out of a collapsed tunnel is very scary. They’re less effective when they’re running down hills, bouncing about and looking like they’re wearing fat suits. But the biggest surprise is reserved for the cliffhanger, when it turns out that these Yeti aren’t the monsters we thought. They’re robots.

Next episode: The Abominable Snowmen – Episode Three