This is still witty: Solon enjoys mocking Condo’s attraction to Sarah Jane, ‘Oh, he’s such a romantic’ (before adding, ‘That’ll do she doesn’t like it’), and can’t even resist making an ‘irresistible’ pun about Morbius’ crowning irony (‘Fool,’ snaps back an unamused Morbius). The prosaic explanation for the death of the Flame of Eternal Life (soot), and Morbius’ gloriously quotable rant (‘Even a sponge has more life than I!’) are superb. But Holmes also introduces the same kind of philosophical angle that lifted Genesis of the Daleks.

‘Death is the price we pay for progress,’ the Doctor tells Maren even as he restores the Sacred Flame to the Sisterhood. Karn is unchanging, a planet trapped in a state of decay. Entropy increases like soot. The quest for immortality, ‘The impossible dream of a thousand alchemists’, is a Bad Thing. Those who seek to live beyond their time, like Maren, Morbius and their followers, are bitter, twisted creatures, set in their ways as times change around them.

I love the way this episode gets darker as it goes along – reflected in the symbolism of night falling on Karn as Solon prepares to conduct his final experiment. As Morbius screeches at him, and Condo recognises his own arm in the gallimaufry creature Solon has assembled for his master, this gets very gruesome indeed. Solon guns down Condo while the brain slops messily onto the floor, and Sarah is press ganged into assisting with the grisly transplant operation. Doctor Who has rarely been quite this graphic. I also love the progression of each cliffhanger – Part One ends with Sarah menaced by the body; Part Two by the brain, and now Part Three ends with the reassembled Morbius advancing on her.

Next episode: The Brain of Morbius – Part Four