Sticking with the end of an era feel of Season 11, this episode is the closest thing the classic series has to those RTD’s season-finale reunions like Journey’s End. Not only does it bring back Mike Yates, to give him a chance of redemption ‘after that Golden Age mess’, but also Jo Grant – at least, a letter from the Amazon written in her distinctive voice, which means she’s present even if absent. As such, this isn’t just a swansong for Pertwee, but for his entire team.

It’s also incredibly sweet. The Doctor is, slightly weirdly, investigating psi powers as if he’s still trapped on Earth and has nothing better to do. This initially involves a trip with the Brigadier to see some tatty revue with an off-colour comedian and an exotic dancer, leading to some great visual comedy for Pertwee and Courtney. Later, the Doctor invites the clairvoyant act, “Professor” Clegg (apparently cosplaying the first Doctor), to his lab for more tests in some sort of hairdryer device. These scenes are all lovely, another chance to include Barry Letts’ favourite effect – the Drashigs, and to give Benton the funniest line: ‘Doing a bit of hairdressing on the side?’. The point of all of this preamble, which is charming but quite thin for anyone not fond of the UNIT Fam, is that Jo has sent back the blue crystal that the Doctor stole from Metebelis 3 in The Green Death.

The actual plot is happening many miles away at a meditation centre for stressed-out businessmen, where another Green Death relic, John Dearth (the voice of BOSS, here playing Lupton) is using the power of Buddhist philosophy to summon something in the cellar. Mike has got wind of this and called in Sarah Jane to do an expose for her magazine. I like the show’s ongoing commitment to Sarah’s character brief, and that she’s clearly still freelancing. It’s notable that she doesn’t even interact with the Doctor this episode and has a life and career that doesn’t revolve around him – something not true of any previous companion. Instead, Sladen and Franklin are paired up, and make a much more convincing double act than Jo and Mike ever did, largely because there’s no romance angle and Sarah treats Mike as her GBF.

After a narrow escape from a psychic attack that seems to come straight from The Dæmons, Sarah and Mike meet the placid Cho-Je (Kevin Lindsay in Yellowface, be warned. There’s also a very 1970s portrayal of a man with mental health issues), who signposts the central conceit of the story: ‘This world of samsara, the world of appearance, is the world of change.’ The audience might very well wonder what on Earth all this has to do with the Doctor’s dilettante investigations. The climax of the episode, again ripped from The Dæmons, provides the answer – as the Doctor’s lab is wrecked by an unearthly wind and the Metebelis crystal glows bright blue, at the meditation centre a similar blue light has appeared in the cellar, as a giant spider materialises.

Next episode: Planet of the Spiders – Part Two