There’s a last gasp of Pertwee-era psychedelia when the Doctor plunges into the anti-matter void (which trips him into a Pertwee-style coma). It’s the equivalent of the slo-mo troll battle in The Three Doctors. The rest of this is far less ethereal; the menace absolutely tangible. Presumably some of this is due to the influence of Robert Holmes – at least the character of De Haan, a grumbling working man, absolutely feels like a Holmes type, as does the joke about Morelli’s funeral (‘Morestran Orthodox’). The horror here comes from people doing awful things: Sorenson, obsessed by his own genius, has allowed himself to be contaminated by the planet, transforming into a cross between a werewolf and Professor Stahlman. Salamar is just frightened and out of his depth, desperate to escape Zeta Minor, and willing to bury the Doctor and Sarah Jane alive in the vacuum of space.

In practice, this involves a lot of scenes of Frederick Jaeger staring in the mirror and clutching his face melodramatically, and Prentis Hancock sucking the life out of every scene as effectively as the anti-man drains the marrow from its victims’ bones. The impetus built very effectively in the first half of the story begins to drain away as the script circles around the same few spaceship sets, with were-Sorenson attacking in darkened corridors and Vishinsky spending a lot of time arguing with Salamar.

David Maloney does what he can with the material. The multi-level sets are pretty good, and Maloney includes some neat camera angles (like pointing down a staircase) to add some visual interest and depth to what – in the wrong hands – could have looked as flat as the Ark. And the script isn’t devoid of good bits: lines like, ‘We must leave this planet before night’ are pleasingly chilly, and the cliffhanger is strikingly horrid. There’s plenty of incident, but not much sense of progress,

Next episode: Planet of Evil – Part Four