Matthew Sweet pointed out that Robot is as near as the show ever got to a TV Comic strip. Similarly, The Sontaran Experiment comes close to being a World Distributors annual story: a slight, and slightly off-beam take on the show, where the Doctor says things like ‘You unspeakable abomination!’ and Harry threatens to ‘knock his bally head off!’ There are a lot of exclamation marks in the script: ‘Worm!’; ‘Murdering swine!’; ‘Come to your death!’. After last episode’s set-up it turns out there isn’t actually much of a story, just Field Major Styre refusing to hand in his homework to the Marshal because he’s too busy torturing the human ants.

It’s as if, knowing this was going to be a 50-minute story, Bob Baker and Dave Martin abandoned any ambition. Whereas previous two-parters The Edge of Destruction went experimentally weird, and The Rescue was a chance to focus on the first new regular, this consists of a noises-off invasion fleet and a collection of torture scenes, which barely build on each other, to fill up the episode. Vural reveals he’s a traitor without any real prompting; Sarah is subjected to some fairly unscary scares, and Harry wanders about some rocks until the Doctor challenges Styre to single combat (another off-kilter moment that properly belongs in an annual, even if you could just about see the third Doctor doing it).

It’s not unlikeable, but it is entirely disposable, a bit of fluff between two more substantial pieces. There are a couple of hints that Robert Holmes has conceived the fourth Doctor more like Troughton than Pertwee (he talks about the 500 Year Diary, and some notes about Sontarans – or maybe this is part of a long game for The Two Doctors). Featuring a Kinda-style rubber snake and a reference to Experiment IV, I’m surprised no-one has claimed this was written by Kate Bush.

Next episode: Genesis of the Daleks