Steve Pemberton and Reece Shearsmith on the return of Inside No 9

It could be the biggest surprise yet for the masters of the shock twist.

Reece Shearsmith and Steve Pemberton say they are switching from darkness to silly for the next series of Inside No 9.

Or should we say next series but one. For the pair are about to start shooting the fourth series of their acclaimed anthology series, just as the third hits screens.

Of the scripts they have just written, Pemberton laughs: 'It's sillier. That's the surprise of series four. We need some laughs!'

"It's much lighter,' Shearsmith agrees. 'This [series three] is quite a dark series, although there are lighter episodes in it - we've gone much lighter in the fourth series.'

Not that humour is ever far from their twisting half-hour stories, but their determination to keep their audience hooked has led them into some dark alleys.

Shearsmith says: 'As an experiment, we tried to write something that was just completely BBC One, just writing a funny thing. It was fine, but it felt that it was lacking.

'Not that it's easy to write just for BBC One, but it was just surface comedy and not turning on its head. Not that there always has to be a twist, but something that's just a little bit deeper. You need something else. We're never happy with just the surface.'

As an example, he said the very first episode of Inside No 9, The Wardrobe, was originally more straightforward before they added a sinister secret.

'It was fine as an idea of a game of Sardines with various characters joining and filling the wardrobe. We wrote that version and then it felt lacking in any drama, any deeper resonance, so that's when we went back in and put in this dread of something that happened in the past. And suddenly that felt like that's what we do now.'

'For us it's all about the narrative,' Pemberton adds. 'It's all about taking that half hour and weaving the story that takes you on the longest journey. And something big has to be at stake, because they are one-off episodes something has to happen at the end which has to turn everything on its head. That's what it's all about.'

So for all the freedom the format gives the pair to experiment with different forms and characters, there is a defining tone to all the disparate episodes.

'They've all maintained a claustrophobia,' Shearsmith says. 'They are all often in real time and you rarely ever leave the room or house that we set them in. That's it's own problem and challenge as well to try to keep the narrative moving on when you can't leave it.

'The exercise is "can you sustain that one idea?",' Pemberton adds. 'You just need a spark that interests you. They are like writing exercises.

'We are just two people but we try to do as many different genres as possible and as many different ways of telling stories and not repeating ourselves, that's important.

'At the beginning of each series and the beginning of each episode, we sit down with a completely blank canvas. We don't tell anyone what our ideas are, we just sit and think and we'll reject a few, and then something will catch our eye.

'To give an example in the new series there's one we decided to write in iambic pentameter. We thought, "What a stupid idea - let's do it!'

'But it's got to be driven by the material, really. We definitely like to experiment but it's got to be right for the episode. It would be wrong to impose something. We've done one in series four that's in reverse chronology, so that was quite interesting, quite challenging. That's what you can do in an anthology, it's much harder to do that in a regular series. We enjoy setting ourselves those challenges.

'Inside No 9 is something that could keep going and going. But if we start repeating ourselves then that's the time to get out because hopefully the audiences are still surprised by what we do and that's quite the challenge.

'Going into the fourth series, a lot of the ideas we've had have been in our bottom drawer for a while and our bottom draw is getting a bit empty now. So it is harder – but then it is quite freeing. I think it's just hard to start. Once we've made a start we find ways within the story that will surprise ourselves as we're going along. We never quite work out what's going to happen until the very end, we just start writing and halfway through we think, "Oh, this could happen now"or "that could take this twist". It's hard changing it up every single week.'

'By the end of the fourth series we'll have written 24 pilots,' Shearsmith adds. 'It's a prolific amount of ideas to keep being fresh about.' But he admits the freedom has its own problems, that writing to a more rigid format. 'We have created a platform where we can do anything… but parameters sometimes help you because you can't do certain things.'

One parameter is the half-hour time slot, which the pair relish. Pemberton says: 'A lot of these kind of things would be stretched to an hour and I think what we've learned to do is to tell quite punchy stories. You wouldn't believe what you can fit into half an hour. It's a great format. A lot of things I think are over-stretched to feature-length or to an hour when they would be much better as a nice tight half hour.'

The anthology format also means a different cast each week, and Shearsmith said that although they never write with particular actors in mind – not even themselves – they have ended up with great names because the job is 'very appealing' for actors.

'It's a week's work; it's good quality - I think – and when you read scripts it's nice to get a one-off that's an enjoyable little tale. So I can't think of anyone who's said "no, it's not good enough for me". Everybody's wanted to do it.'

And the constantly changing cast 'rejuvenates us', he added.

Perhaps the most distinctive of the forthcoming third series – whose opening episode The Devil Of Christmas was screened over the festive period – in Empty Orchestra, set in a karaoke booth,

'It's sort of a musical as there is music all the way through it,' Pemberton says. 'Normally in karaoke scenes in things you see people sing the first two lines and then it cuts to something else. We sing the entire song because we're never leaving that room.

'I would love to do a proper La La Land style musical. But I think for now Empty Orchestra hits that. And the idea of doing a love story was very appealing and that's kind of what that is…'

Producer Adam Tandy admits that episode was difficult to film, making sure the songs matched up in the edit and filming each scene from four different angles, by removing one wall of the set each time –  a challenge for a man whose job it is to deliver Shearsmith and Pemberton's vision on a tight budget.

'Occasionally an idea will be too big,' he admits. 'There was a script from the first series that had some CGI in in, The Harrowing. Actually, we changed it for other reasons, but we would have struggled on our budget to include a CGI creature.

'Some episodes are cheaper than others, the Devil of Christmas was probably a folly in that respect, it cost us more than an average episode. That was simultaneously the most fun to make but also the most nerve-racking, because it involved so many elements that could go wrong.'

'But we try to find a tone or a way of shooting or something that's different within a series - you'll be hard pushed to point to tonal similarities between any two episodes. Also the writing. Just looking at the first seres, there's a bit of Pinter, there's a bit of Ayckbourn… you know it's all sorts of different things.'

• Inside No 9 returns to BBC Two next Tuesday at 10pm, with The Bill, in which diners including Jason Watkins and Philip Glenister fight over who should pick up a restaurant tab.

Our favourite series 3 episodes

PRODUCER ADAM TANDY

'Diddle-Diddle Dumpling, the one with Keeley Hawes. It's about a man who finds a shoe in the road outside his house and tries to get it back to its owner. As a half-hour descent into one man's madness, it's quite extraordinary, and it's been shot in slightly Bergmanesque style - very symmetrical framing and very long held shots that just watch this man going slightly loopy.'

Pemberton says he came up with the story as he was walking to work, racking his brain for story ides, when he spotted a shoe in the road and started wondering 'what would happen if someone became obsessed with returning it'. By coincidence a couple of days later Shearsmith found a solitary shoe, too. Not a matching one, sadly for intrigue fans.

REECE SHEARSMITH

'I really like the Riddle Of The Sphinx, about a crossword compiler, for the gothic way it twists and turns. And Devil At Christmas because that was born out of the heritage of this show, coming from that era. So we thought, "Shall we just do one?"

STEVE PEMBERTON

I'm going to go for Empty Orchestra, which is an absolute joy of an episode. I get to sing a bit of Rainbow and it's very different to everything else we've done up to that point. I hope people really enjoy it and don't go "Aw, I really wanted them all to blow up at the end!" We've done enough darkness, so it's good to do something a bit lighter and a bit fun.

Published: 14 Feb 2017