After the lushness of The Masque of Mandragora this is a clear step backwards. It doesn’t help that the opening scenes on Kastria are the worst bit of the episode as a plastic-looking spaceship wobbles into view in front of a BBC starfield before some quilts called King Rokon and Zazzka shout at each other about the obliteration module of ‘Eldrad the traitor’. It’s the kind of opening Doctor Who starts sending up itself when Douglas Adams takes charge, and it hangs this off a distinctly shaky peg. The prestige of the previous story disperses as completely as Eldrad.

It’s much better once the Doctor and Sarah Jane arrive on Earth. This sequence is charming: mucking about playing cricket with rocks and joking about South Croydon, and making fun of the alien planet/quarry tropes. They look as comfortable together as the tenth Doctor and Rose – which can’t have been lost on RTD – and share their breezy sense of indestructibility at exactly the moment it’s going to be brought crashing down around them. The twist into real-life is brutal: digging Sarah out of a rockfall, the Doctor looks stricken while Abbott the foreman witters on about taking responsibility for insurance purposes. I love seeing the fourth Doctor interacting with normal people: getting his arm checked out at the hospital and having to go back to the quarry to further investigate the provenance of the mysterious stone hand Sarah was found clutching.

While the Doctor investigates alien possibilities, Sarah is living them. Like Katy Manning, Sladen’s being gifted with a proper leaving story which means she’s being given another, bigger opportunity to play an evil version of Sarah. ‘Eldrad must live,’ she intones as she raises her own glowing blue crystal directly to camera. Interestingly, she doesn’t do this like she’s been brainwashed (like in the previous story), but in a strangely flirtatious way. She chews her finger coquettishly as she tempts the Nunton nuclear reactor’s gate security guard out of his booth to zap him. These sequences are great: Lennie Mayne shoots them with a fisheye lens to make them additionally disorienting. The cliffhanger of Sarah going inside the reactor is brilliant.

Next episode: The Hand of Fear – Part Two