After the punchiness of the first three episodes this is almost sedate. Even so, it crams the reveal of the Master/Nestene plot; an RAF missile attack on the Autons’ invasion coach (!); the summoning of the Nestene Consciousness; the Master’s change of heart, and a final couple of scenes that establish the new status quo for Season Eight.

Having kept them apart throughout, the episode also finally has the Doctor and Master meet. ‘You’ve come here to kill me of course,’ the Doctor comments coolly as the Master waves his TCE – prompting Jo to hurl herself in front of the Doctor while simultaneously giving away the Brigadier’s plan. This kind of impetuous self-sacrificing streak is going to recur through the season, but what’s most impressive is Jo’s ability to be both a bit useless and utterly invaluable at the same time. Later, having got herself and the Doctor captured, she shows off her escapology skills and gets them freed. Four episodes in and she’s already established herself as a crucial element to the show’s new format.

Captain Yates is less obviously crucial. Aside from being a familiar face, he doesn’t really do much except make fatuous remarks (‘The Brigadier wants to know if the daffs are dangerous’). And having been virtually a co-lead in the last season, Nicholas Courtney’s relegation to the Doctor’s stooge is sad. But the show is now no longer about a paranormal military investigation squad with a mysterious alien scientific advisor; it’s about the Doctor and Jo battling the Master. Plus the increased focus on Chekhov’s TARDIS – the Police Box is conspicuously back, even if it’s not working yet – isn’t accidental. Inferno pointed the way to the Doctor getting the TARDIS to take him to other times and places. Terror of the Autons doesn’t immediately follow up on that, but the possibility has been dangled before us.

This is a really weird story. In a lot of ways it’s an in-your-face reformatting by a new producer: The Leisure Hive of the 1970s. It’s a bit sillier and consciously quirkier than Season Seven (e.g. the shootout with the carnival Autons; daffodils as an invasion tool), and the regulars are becoming more extreme versions of themselves. As a producer and director, Barry Letts also brings a sense of what can and can’t be achieved effectively (the climax here doesn’t feature Pertwee gamely hurling himself into a giant limp tentacle as in Spearhead from Space, rather the vague outline of a Nestene octopus) even if he is a bit over-fond of CSO.

The ending is a little bit of a damp squib – the Master has a ridiculously sudden change of heart, helps the Doctor repel the invasion, then makes a Blofeld-like exit. But in context it makes complete sense: it’s not really the end of the story, but the introduction to a new set-up with a regular villain and a slightly more vivid, but less “realistic” set of heroes. Personally it’s a Doctor Who story I never tire of, even if it’s not one of my absolute favourites.

Next episode: The Mind of Evil