‘Hey, that’s good, isn’t it? “The Crimson Horror”.’ Mark Gatiss’ best script to date plays to all his strengths in macabre comedy, like the Curse of Karrit Poor section of the League of Gentlemen Christmas Special. He also throws in elements from Carry On Screaming (people being turned into mannequins after a dip in some bubbling liquid), and – probably in tribute to Dame Diana Rigg – The Avengers (Jenny going undercover and changing into a leather fighting suit). The result doesn’t tread new ground, but it’s the most straightforwardly entertaining episode since Dinosaurs on a Spaceship.

Mostly this works because it’s fun. The Doctor is delighted to be confronted with such a Penny Dreadful problem – “the Crimson ‘Orror!”; Rigg’s blood and thunder performance is perfect (particularly her curiously girlish behaviour towards Mr Sweet, as she sprinkles spilled salt down her bodice), and the Thomas Thomas joke is corny but executed brilliantly. I love the imaginative touches like the final image preserved on the victim’s eye; the huge gramophones faking the sound of industry, and the scratchy sepia-tinted flashback that explains how the Doctor and Clara got involved. The bathos of the Mr Sweet reveal is masterful.

I’m also a fan of this unfolding as a Doctor-lite episode. Photo aside, he doesn’t turn up until 14 minutes in, which means the first third of the episode plays like the back-door pilot for a Paternoster Gang spin-off (Vastra as the brains, Strax as the brawn, Jenny as the inside woman). It means the characters must investigate rather than relying on the Doctor’s encyclopaedic knowledge and psychic paper. And their reaction to Clara’s mysterious (from their point of view) resurrection is probably the neatest example of the series’ ongoing story.

The only downside is the ongoing ick the Doctor seems to have acquired this half-series (he snogs Jenny then does a sonic screwdriver “erection” gag when she gets changed, kisses Clara and kisses Ada), but handsy old Time Lords aside this remains a highlight of the 50^th anniversary year.

Next Time: Nightmare in Silver