‘Our genius has been abused.’ So, the climax of this boils down to the Doctor learning Mestor’s true plan and deciding to assassinate him with poison. He’s only prevented from doing so by Mestor’s mind powers, at which point Mestor informs the Doctor he intends to transfer his brain into the Doctor’s body, but before doing so he will demonstrate what he’s about to do by transferring his brain into Azmael’s body. The Doctor then dissolves Mestor’s old body with acid (another Season 21 death by gloop), and Azmael commits suicide.

This is utter nonsense. The mind transference plot could have been a whole serial in itself – and, handled better, could have provided an explanation for the Doctor’s bouts of murderous insanity: it was Mestor trying to exert control. As it is, it just seems thrown in at the last minute as a way to defeat the slug. It also means in his first story, the sixth Doctor’s first resort to dealing with a villain is to murder him. Sometimes, in future, he even gets lucky and manages it (Shockeye, your time is coming). I suppose there’s an honesty to this – Saward doesn’t try to dress it up as an accident in a tussle or anything like that – but if the Doctor is now a time-travelling assassin why not just give him a gun? “Doctor, Davros is going to resurrect the Daleks!” *BANG!*; “Doctor, the Master is going to try to take over the universe!” *BANG BANG!!*; “Doctor, the Silurians are-” *BANGBANGBBANGBANGBANGBANGBANG!!!!!*

Mestor, like pretty much everyone she ever meets, suddenly declares he lusts for Peri: ‘I find her pleasing.’ What? Hugo, a huge waste of Kevin McNally, gets to do a Steven Taylor and become leader of a planet he’s been on for about an hour. The Doctor has developed psychic powers: not only did he sense evil in Part Two, now he can sense it’s coming from the hatchery. Of course, there are tolerable moments (the Doctor’s first meeting with Mestor, and his farewell to Azmael) but this is the archetypal curate’s egg – obviously and entirely bad.

‘I am the Doctor, whether you like it or not.’ Season 21 on the whole improves over Season 20. This is the low point – a risky premise (make the new lead a bit spiky, and only allow the audience a week to warm to him between introducing him and ending the season) made disastrous by another piecemeal script and baffling design choices. Elsewhere, the weakest stories are better than the weakest parts of Seasons 19 and 20, and the best stories (Frontios, The Caves of Androzani) contain pretty much the strongest material Davison is given across his tenure. Season 20 in particular suffered from a lot of vague and gauzy threats, whereas this has much more tangible baddies. It’s also more brutal than the show’s been since about 1976. Still, with a season break coming up there’s a chance for JNT and Saward to reassess and come up with something heroic and accessible to open the next series.

Next episode: Attack of the Cybermen