A good chunk of this episode feels oddly familiar, like a jumble of influences plundered from other stories. The TARDIS’ arrival on a beach, where the Doctor and his friends much about before getting shot at isn’t a million miles away from The Enemy of the World, and along with the general high security paranoia and the theft of a file by an unseen saboteur suggests this might be another espionage thriller. But then there’s the relationship between Chief Robson, the governor of this base under siege, who’s a familiar General Cutler type: a gruff despot, like Clent or the Gatwick Commandant. And the idea of a monstrous something lurking hidden in the pipes, living on poison gas, is right out of The Macra Terror – with that story’s Controller, Graham Leaman appearing as Price.

In short, there’s nothing here that is especially new: a feeling apparently shared by Jamie and Victoria who complain they’re always landing in England. At least the regulars get some fun business, working together to escape their cell. Victoria shows some gumption by trying to pick a lock with a hairpin, and Troughton’s trawlerman look is a nod back to his old habit of dressing up.

I also like the ominousness of the heartbeat in the pipes – and the horrid image of trashing, slimy seaweed tendrils bursting out of the foam to menace Victoria – or even just lurking, waiting to be picked up by Maggie Harris. The domesticity of the base, with its residential block, and a family life for the crew (or at least Harris) is also a nice change from the normal collection of gruff men and hyper-efficient women.

Next episode: Fury from the Deep – Episode 2