‘Is everybody in this conspiracy,’ asks the Brigadier as the Doctor outlines General Finch’s part in the plot to frame him. The answer, pretty much, is yes. But that’s in part what gives this a modern, paranoid thriller style a long way from the criticised cosiness of something like The Time Monster. This time there’s no Master plotting world domination, or alien invaders to be beaten back. It’s all on us. Even our friend Mike Yates has fallen for the comfortable panacea offered by wiping the slate clean and starting again, to escape from a world that’s ‘too complicated and corrupt’.

Of course, it’s all built on a lie. ‘There never was a golden age,’ the Doctor says sadly. The conspiracy’s new start is built on a lie. They’re not going back to a simpler, better time, because they’re already taking the complications and corruption of the modern world with them. ‘I had to tell a story that would be acceptable to people like Adam. The sort of people I wanted to recruit,’ Grover bleats to Mark and Sarah as he tries to justify his actions. Hulke’s script has no truck with misplaced nostalgia, while retaining a fairly clear-eyed (and very Socialist) view of the real issues that need to be resolved: ‘It’s not the the oil and the filth and the poisonous chemicals that are the real cause of pollution, Brigadier. It’s simply greed.’ ‘Hmm,’ replies the conservative Brigadier sceptically.

Invasion of the Dinosaurs isn’t my favourite Pertwee serial, but I think it’s the best use of the UNIT Fam, one that suggests some real character growth rather than using them as the Doctor’s chorus line. The Brigadier is back to being a serious, intelligent military leader (although I wonder when he forgot The Web of Fear: ‘I never thought I’d find myself blowing up a tube station’), arguing over the jurisdiction of his prisoner with General Finch and refusing to turn his back on Yates (giving him the opportunity to resign with dignity is a very real, human touch). Benton’s loyalty to the Doctor and Brigadier pays off in his willingness to risk court martial by punching Finch and letting the Doctor escape. And Yates’ experiences in Llanfairfach have presumably led him to a point where he sees mankind as a greater threat to the Earth than the Master. His willingness to sacrifice himself for his ideals (‘I’m not important’) is consistent with his principles: he hasn’t just become a convenient baddie. There are more UNIT stories to come, but this feels like the final word on the classic line up. It’s fitting that it should be written by Malcolm Hulke, whose serials have been the bedrock of the Pertwee seasons, and who remains along with Terry Nation the most significant Doctor Who writer never to be script editor.

This also serves as a great second story for Sarah Jane. For about half the story she’s entirely separated from the Doctor, leading her own attempt first to expose the conspiracy, and then to save the duped people on the “spaceships”. Her journalistic desire to uncover the truth finally leads her to elicit a confession from Grover, revealing the reality of their situation to the “colonists” – which becomes a crucial part of stopping Golden Age from succeeding when they invade the control room and overpower Whittaker. Her reunion with the Doctor in the final minutes is when she actually becomes a fully paid-up companion – and the Doctor has to tempt her into joining him with promises of a trip to Florana (he’ll have to keep doing this – in Robot, and then in Terror of the Zygons). We haven’t seen such a prolonged flirtation before – the first three stories of Season 11 flow into each other in a way that hasn’t really been the case since Ian and Barbara. And it’s so effective, RTD reintroduces it with Rose and Martha.

So, 10 episodes in and, episode for episode, Season 11 is shaping up to be the best season of Doctor Who ever. What could possibly go wrong?

Next episode: Death to the Daleks