Be careful what you wish for.

Ever since the first episode of Inside No. 9, the latest comedy series from one half of The League Of Gentlemen, there has been an unholy chorus of voices demanding a return to the darker, more gothic tones that were scattered across Royston Vasey. You know, the early, scary ones.

Well, last night, they got exactly what they asked for. And in spades. The sixth episode is called ‘The Harrowing’, and it’s fair to say that it’s a very apt title.

Aimee Ffion-Edwards (Skins) is excellent as schoolgirl Katy, a Nice Girl To Whom Bad Things Should Not Happen, and there’s great support from Poppy Rush as her best friend Shell, who idolises her out of all proportion, almost to the point of worshipping at her altar. Katy is to be paid £88 – a culturally significant number – for a special babysitting job in a crooked house where nothing ever happens, not even a phone signal.

Hector and Tabitha are the brother and sister who have employed her services, played by Reece Shearsmith and Helen McCrory (Harry Potter), carefully pitching their characters to seriously unbalance the style of the piece, but not so cartoon that the episode actually capsizes.

It’s a gamble that pays out: Katy and Shell appear to have wandered from the real world into an entirely different arena: a battered paperback of Pan’s Horror Stories by way of Helena Bonham Carter. This works exactly because Katy’s character is so believable, so logical, so at odds with the altogether ooky personas creeping out of the dark shadows.

The cartoonish nature of Victor and Tabitha makes what happens after the bell tolls not only scary, but downright upsetting. More than that, it’s wrong. Katy is a bright, witty girl who does babysitting. Her moral centre is that she’s basically a good girl, who wishes to please. It’s also her fatal flaw.

Such moral ambiguity means that one of the most genuinely laugh out loud moments of the episode happens at the end – the very end, at the close of the credits – when a title card reminds us that this has been a production of the BBC comedy department. That’s no insult: there are jokes in the preceding half hour (and some very good ones), but what has just happened isn’t comedy. It’s out and out horror.

As this series draws the curtains for the last time, it’s appropriate to make special mention of director David Kerr, whose six episodes are like so many scattered calling cards: each half hour entirely different in tone, structure and even visual tricks and camera angles.

If Jeremy Dyson was the unsung hero of the League of Gentlemen, it would be fair to claim similar status for Kerr. Hopefully, he’ll be called back into service next year. That’s if he isn’t snaffled up by others. On the strength of these episodes, he’d be equally at home with Quatermass or Keeping Up Appearances. Or a crossover episode of both.

We get not only the telly we ask for, but the telly we deserve. But you can train a viewing nation’s palate, too. Serve up mainly Splash and TOWIE, and that’s what sates us. But occasionally, we want something more demanding, clever and memorable. We’re lucky to have Pemberton and Shearsmith, and it’s good that they’ve left the key under the mat for a second series.

Otherwise we’d have to lock them up.

Aired at 10pm on Wednesday 12 March 2014 on BBC Two.

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