It’s impossible now for any fan to experience this episode without the foreknowledge that the ‘Planet of Giants’ is actually England, and that this is an adaptation of the original ‘minuscule’ pilot storyline that they’d been toying with making for nearly a year. But trying to get into the spirit of it: to date, every new adventure has fallen into one of two categories ‘adventures in time’ or ‘adventures in space’, and every one of the former has alternated with one of the latter (The Edge of Destruction is an exception because the time travellers don’t leave the TARDIS at all). At the end of The Aztecs, the production crew explicitly called out that the next episode would be an ‘adventure in space’ thanks to the onscreen next episode caption. Prisoners of Conciergerie similarly cued the audience to expect an outer-space serial by playing a caption card ‘Planet of Giants’ over a starfield. Looking at the Radio Times publicity material for this episode, other than drawing a comparison to Gulliver’s Travels (which is pretty evident from the title) there’s no hint of the bigger twist – this is actually a contemporary Earth adventure.

Not that Louis Marks milks the mystery for too long – the explore phase of the adventure, which a few months ago would have taken the whole 25 minutes, is done and dusted in half that time. After the obligatory scene of the TARDIS malfunctioning (see also The Dead Planet, The Edge of Destruction and The Roof of the World), nothing seems to be too amiss – except that the scanner blows its tube. So the Doctor (still wearing his Regional Officer’s cloak) and Barbara head in one direction, and Ian and Susan in the other. Encountering a lot of dead insects (a worm, an ant and a bee), Ian wonders ‘what sort of a world could produce an insect that size’ (he’ll get his answer in a few months’ time) before surmising that they’ve arrived in some ‘crazy exhibition’. But the Doctor and Susan have separately worked out the truth: in a very well-directed sequence, Mervyn Pinfield cuts between the two of them explaining to Barbara and Ian that the ‘space pressure’ has reduced them to roughly the size of an inch.

This revelation comes 11 minutes into the episode: in that time, we’ve had the TARDIS going bonkers, the exploration of an “alien” planet, and a big reveal. And having dropped the bombshell, Marks then introduces the complicating factor: a thriller plot, which Ian stumbles into when he accidentally falls into a matchbox that’s picked up by one of the normal-sized people. The thriller is exactly like something from the contemporary crime shows that Marks had both written for and script edited, and usually focusing on the exciting world of horse racing or antique dealing or – here – insecticides.

Marks’s script quite neatly cuts between the confrontation of jobsworth government scientist Farrow and ruthless entrepreneur Forrester, and the time travellers. As Farrow reveals that the insecticide DN6 is too effective – killing ‘many insects which make a vital contribution to agriculture’, the Doctor and Susan experience the effects close up, and are equally concerned: ‘What worries me is all the different things it’s killing. Things that fly in the air, things that move on the ground, things that move under the ground. It’s so indiscriminate.’ Throughout, Marks and Pinfield make this a particularly pacey episode through this collage of scenes, rapidly cutting between parallel conversations to deliver the exposition in an engaging way. Combined with some impressive visual effects (although William Russell having to act in front of a giant blow-up back projection of Farrow’s dead face is a bit of a stretch), and a script that’s attempting to give some more balance across the four regulars (Susan’s notably better used in this than she was in the previous six episodes), this is very good indeed.

Other things I noticed:

• The Doctor’s grumpy dismissal of Ian and Barbara’s questions about the TARDIS malfunction feels like a callback to his early characterisation, but it’s immediately balanced by his charming apology: ‘Oh, my dear Barbara, was I rude to you just now? If so I’m so sorry. I always forget the niceties under pressure.’
• Susan says, ‘The doors of Tardis opened’ – the convention of calling it ‘the TARDIS’ hasn’t yet been established.
• The Doctor’s line ‘Death has it’s own particular posture and appearance’ is very evocative, and a bit creepy.

Next episode: Dangerous Journey