After the army were drafted in for The Mind of Evil and the Navy for The Sea Devils, this time it’s the turn of the RAF. It’s a bit of a half-bothered effort though, with one lo-tech helicopter lobbing some bombs out of the door. Where are the Harrier jump-jets with cruise missiles? It’s a good sequence, though, in a serial that’s already well above its quota of iconic images. It’s also a nice twist that UNIT and BOSS share the same goal: the elimination of the maggots. They aren’t part of a grand plan to take over the world, but an unintended consequence of Global Chemical’s pollution and ruthless efficiency/corner cutting.

This is all explained to the Doctor during his chat with the BOSS: a genial-sounding captain of industry that just happens to be a computer. Pertwee plays the Doctor as secretly delighted that the shadowy leader of Global Chemicals is actually a mind-controlling supercomputer, and is evidently very tickled by its acronymic name. The whole interrogation sequence is a triumph, recalling Hartnell’s gleeful trouncing of the Moroks in The Space Musuem, or Troughton’s confrontation with the Krotons, with the Doctor entirely unfazed by BOSS’s efforts at mental domination, and essentially acting as flippantly as the fourth Doctor. BOSS isn’t a walkover though, it can give as good as it gets in banter: ‘As far as I can gather from your computer record at UNIT, the difficult thing is to stop you talking,’ it quips to the Doctor. It paints a picture of an ordered, affluent society free from want and fear (and from freedom, as the Doctor points out) organised and directed by Global Chemicals.

Pertwee gets tonnes of great stuff to do in this episode: having escaped with the help of the undercover Captain Yates, he makes a low-speed getaway on a milk float, uses his sonic screwdriver just like a magic wand to hold back the maggots and rescue Jo and Professor Jones (you can see where RTD got the idea), and make use of the blue crystal he acquired on Metebelis 3 to de-program a freshly-brainwashed Yates who has been sent to kill him. This last scene both gives Richard Franklin the first worthwhile material he’s had in two years, and makes what seemed like a jokey sequence in the first episode into an integral part of the story. And with Professor Jones’ infected maggot bite adding urgency, this is a fifth episode that creates some real momentum into the finale.

Next episode: The Green Death – Episode Six