This episode is starkly split between the futuristic control rooms of the Euro Gas facility and the amazing psychedelic domesticity of the residential block. Robson stamps around control bullying Harris and bashing heads with Van Lutyens, and everyone very earnestly talks about impellers and pipelines and gas flows like this is a knock-off of The Power Game. Meanwhile, in their apartment, the Harrises talk to each other like they’re in Brief Encounter (it’s all ‘darling’).

It’s a slow episode whose main highlight is the one substantial fragment that still survives – the scene of the sinister Oak and Quill, Doctor Who‘s own Wint and Kidd – overwhelming Maggie with what seems like their appalling halitosis. It’s directed very well, with fades between cameras focusing on the choking Maggie and the gas hissing from Oak and Quill’s mouths, which looks like a quite promising indication that this was directed very well. And with Dudley Simpson’s dissonant incidental music adding to the unease, plus some nicely foreboding dialogue (‘It’s down there… In the darkness… In the pipeline… Waiting’) this has a creepy edge that continues the show’s fifth season pivot into horror.

But for all that, there’s really not a lot of substance to the episode, and the plot logic seems driven more by the need to string it out for six weeks than any genuine forward momentum. For example, having Oak and Quill not only faff about pretending to be repair men rather than getting on with their mission, but then abandon the overwhelmed Maggie to be found by the Doctor feels like unnecessary heel-dragging. And there are an awful lot of scenes of men arguing about pipes. Still, you have to admire Maggie’s home décor: it’s enough to make the episode worthwhile.

Next episode: Fury from the Deep – Episode 3