The episode continues the slow burn, but with a clear sense of direction and momentum. The first half concerns Khrisong’s desire to protect the peace of the monastery, even if it means he has to fight. It’s deft characterisation that means the main antagonist of the episode is also entirely sympathetic – he’s devoted his life to defending the monks, and it’s ultimately his bravery that nearly bags the Doctor a control sphere for study.

But what Khrisong doesn’t appreciate is that in barring the gates of the monastery to stop anyone from leaving, he’s trapped the danger inside with them. A control sphere is already making its steady way back towards the captured Yeti, and its inexorable progress through the course of the episode gives a real sense of imminent menace, especially while the oblivious monks make a spirit trap to contain the monster’s evil – a trap the audience knows full well is going to be useless against a revived Yeti.

The master Padmasambhava, hidden in the inner sanctum, is clearly in control – cleverly, this is established through him moving Yeti chess pieces around a map as if he’s Borusa playing the Game of Rassilon. Clever, because by showing an army of Yeti pieces it saves having to make dozens of actual costumes.

In a twist towards Lovecraftian cosmic horror, Padmasambhava reveals the real guiding hand:

PADMASAMBHAVA: The Great Intelligence will focus upon this planet. Soon it will begin to grow and, at last, take on physical form. At last its wanderings in space will be at an end

Haisman and Lincoln have mixed robots, disembodied alien consciousnesses, Tibetan myths, and Empire adventure fiction. These are exactly the kind of incongruous juxtapositions Doctor Who excels at, and it elevates this story’s scale and significance above the slightly more mainstream cyborgs on the Moon adventures of Season Four.

It helps that they inject a strain of dark humour that works very well: after Khrisong is injured by Yeti when trying to recover a control sphere, the Doctor rather callously makes the James Bond quip, ‘They came to get their ball back.’ And Padmasambhava is equally wry: ‘It would seem that the Yeti have caused some little upset at the gates.’

The second half of the episode sees several characters leave the uncertain safety of the monastery to venture into the mountains – the Abbot on a mission from his master, Travers searching for the real Yeti, and the Doctor and Jamie to fetch scientific equipment from the TARDIS. The night filming, with the Yeti emerging from the shadows, looks like it was very creepy indeed.

Meanwhile, inside Detsen we get to see Victoria belie her reputation as a helpless screamer. She’s pushy and imperious towards the monks, and with all the high-handedness of a Victorian Nancy Drew, declares, ‘I don’t like mysteries.’ So far, her role both here and in The Tomb of the Cybermen has been to single-handedly confront one enemy while the Doctor and Jamie tackle the others, and so far she’s far from the useless peril monkey she’s sometimes painted as.

Next episode: The Abominable Snowmen – Episode Four