The Doctor looks genuinely terrified at the start of the episode, as the Animus’ hairdryer descends, but he remains defiant, refusing to be subjected, or terrorised. In Season Two, he’s largely been a deceptively active character in comparison to the more traditionally “mature” lead he played in the first season. He’s recently been engaging in fisticuffs, and generally getting almost as much physical stuff as William Russell. But under the influence of the Animus he seems to be aged, and rendered suddenly doddering. In context, it’s quite disturbing, and it makes the Animus seem like one of the most dangerous enemies yet.

Meanwhile, out on the planet’s surface there’s a bit of a stupid sequence of the Menoptra prancing round singing ‘Zarbiiiiiii’ to perplex the ants. It doesn’t really work. However, the rest of the Menoptra assault is a bit more convincing, with some characterful bits where the Menoptra mourn a fallen comrade (whose corpse lingers in close up).

Inside the Carsenome, the hideous Animus is revealed to be a giant glowing spider creature, plugged into the middle of its web – and encountering it first hand seems to sap the Doctor and Vicki of all their energy. The pair are ensnared in the web as the Animus threatens to drain them of their knowledge – and suddenly (and somewhat unconvincingly) the stakes are raised from the fate of Vortis to the fate of humankind – ‘to pluck from Earth its myriad techniques’ as the Animus rather Miltonianly puts it.

With the Doctor and Vicki incapacitated, it falls to Barbara to lead the Menoptra assault on the Carsenome. She finds the Isop-tope, but almost falls victim to the Animus’ hypnotic voice and deadlights. Only Ian’s arrival, having burrowed up from the roots of the Carsenome, restores Barbara’s hope and allows her to kill the monster. Given how well the Animus has been established even in just a couple of scenes, and despite some decent visuals, the finale plays out rather flat – but then, Richard Martin also fumbled the climactic battle in the last episode of The Daleks, so it’s not like it’s entirely surprising.

The lengthy coda, complete with poetic Menoptra and happily hopping Optera, is slightly laboured, although the idea that there is space for the Zarbi and their larvae in this newly freed paradise, as part of a renewal of the natural cycle of feeding the soil to grow the flower forests, is a quite beautiful ending to a story that has a lot of clunky moments but also a scale and weird grandeur that are almost transcendent.

I’d never properly watched The Web Planet before this episode-by-episode viewing. It’s easy to dismiss as a stupid insect pantomime. But I don’t think that’s fair. Bill Strutton’s script has as much poetry as anything by David Whitaker, and its ideas, and the genuine attempt to portray alien culture, thought processes, environments and biology are as ambitious as anything the show has ever tried again. It’s not an unqualified success, but if it didn’t exist I bet this would be one of the most wanted missing stories of all.

Next episode: The Lion