‘Disappointing, aren’t they?’ Like The Invisible Enemy, this makes a joke of its rubbish “monsters”, although unlike The Invisible Enemy there are better monsters waiting until the end of the episode to make an appearance. I really like this: if the Vardans had just been rubbish it would feel a bit contemptuous to the audience, but it’s all part of the build to that rug-pulling climax and the return of the Sontarans.

Given it was born of desperation, this is really good fun. Tom Baker is at his most “dear old thing”, throwing out one liners (‘I do talk to myself sometimes’, ‘every oligarchy gets the Castellan it deserves’) in a way he never really did until this season. Barring Season 18, this is pretty much how he’s played the Doctor ever since. His double act with the entertainingly bemused Andred is brilliant, he’s worked out how to get laughs from the K9 prop, and generally seems to be quite enjoying this in a way that wasn’t quite so apparent at the start of the season. The moment he enters the Panopticon in triumph, posse behind him, is perhaps the Doctor’s high point.

The cliffhanger is one of the greats and feels more planned than it probably was given the Sontarans were mentioned in Horror of Fang Rock. It doesn’t quite have the frisson of the Daleks or Cybermen would have done, I don’t think (like if in the new series the Doctor turned round to see not Weeping Angels but Slitheen) but I imagine most of the contemporary audience would have recognised them. This continues to be very entertaining indeed.

Next episode: The Invasion of Time – Part Five