Simon Donald’s shapeshifting, frosty thriller is back and pulling no punches. Amanda Nicholls visits cast and crew at Bristol’s Bottle Yard Studios to find out what’s in store for the third and final instalment of Fortitude, airing on Sky Atlantic this month *Warning: may contain spoilers…

Earlier this year, a little bit of Hollywood sneaked into Whitchurch when Sky Atlantic’s not-your-average-Nordic-noir series Fortitude came to Bristol to film part of its finale; complete with movie star Dennis Quaid and Game of Thrones’ Richard Dormer. With the UK leg of the shoot entirely studio-based, the team needed production expertise and plenty of it, plus room to construct multiple sets, and were drawn to Bristol’s brilliant Bottle Yard space to fulfil both creative and practical needs.

ARCTIC WESTERN: Richard Dormer (Game of Thrones) plays conflicted sheriff Dan Anderssen and says it’s been the most emotional, therapeutic shoot he’s done: “Nothing could take me as far into darkness and light as this.”

The concluding season of the smash sci-fi thriller which has also starred Michael Gambon, Stanley Tucci and Sofie Gråbøl, and saw 1.4million tune in to each chilling episode during the second series, is set to hit our screens on 6 December (just enough time to catch up on series one and two, then, if you’ve not seen them). The focus? All the fallout from the mad previous instalments which see shamanistic goings on and dormant prehistoric viruses come back to life via wasps frozen in ancient ice caps – and play with genres from psychological whodunnit to police procedural to seemingly supernatural to ensure audiences are never quite sure where the answers lie.

“We took a risk with the first series, in allowing the audience to believe they were watching Agatha Christie set in the Arctic but realise halfway through that it was actually a horror show,” creator Simon Donald gleefully recalls. “We wanted the audience to be angry and say: ‘What’s happening? This had better be good.’”

“What I loved about the first season was that nobody knows what’s going on,” says Dennis Quaid, who plays grieving fisherman Michael Lennox. “Now, everything is coming to a head and is very intense. Michael has become the town drunk, he’s a misery, but then a series of strange events happen. He meets up with an enchantress who brings him back to life.”

Said siren is one of several new characters for series three, in need of all our thoughts and prayers – because anyone who’s seen the show will know how high its mortality rate is. “It’s more an Arctic western than anything else,” reflects producer Drew Wood when we visit The Bottle Yard where the cast and crew are filming their interior shots, “because it’s about a small town – Fortitude – that nothing much happens to, then all of a sudden everything happens.”

Dennis Quaid returns as grieving Michael Lennox

Simon had written the usual 10/12 episodes’ worth of material for season three, but when it came to actually putting the show’s big ending together, the team faced the challenge of being commissioned to make just four – which, says Drew, simply meant distilling all the best bits to create tight, streamlined chapters brimming with action. “As the series develops there is just so much material,’ he says, “and instead of padding out around 10 episodes it’s just the really good stuff.”

“The scripts wrote themselves in a way that hadn’t happened before,” Simon adds. “For the first time they were ready before we went into production and that was a godsend. Fortitude has been a runaway train, with me on the tracks in front of it, running as fast as I can until production catches me up and kills me…” With big set pieces in each episode, and zero deadwood, it’s all killer no filler this time – and as fans will know, we mean this in the literal sense too – concluding, according to Simon, in a “Jacobean, operatic, bonkers final episode.”

Condensing the show’s climax also meant the crew could finally afford to go out and shoot on location right where the whole thing was conceived – icy Svalbard. “The cold was a big factor; the wind chill brought it down to minus 35 so it was more like an expedition; imagine Mr Fiennes going through the tundra,” says Drew. “We were a first as far as the Norwegians were concerned, in going that far north to do something like this. They’d never had a big drama series come up so far; and there’s a very good reason why!”

Surprisingly, the team had needed to import a huge amount of snow when they were filming in Iceland, but lack of the white stuff wasn’t an issue further up in Svalbard. “We tested the cameras in freezers here then built little enclosures for them with handwarmers and all sorts of things built in so they could stand the low temperatures,” reveals Drew.

SNOW PATROL: Can police officers Ingrid and Petra protect the town of Fortitude?

The change of location really adds a special extra something and cranks everything up a level to make it feel suddenly very silver screen. “It was like the show went home,” says Simon. “There’s an epic quality to all the landscape stuff. The plains are bigger, the weather is staggering, it looks like something James Cameron created; it’s wild. Working in those conditions changed everything; the actors’ performances, the crew – who were like an occupying small guerilla army, it felt that extreme.”

Rock-bottom temperatures weren’t the only threat to contend with; with the native wildlife on the prowl too. “We were surrounded by men with rifles because of the polar bears; you’re very conscious it’s a hostile environment,” recalls Drew. “You can’t die there, you’re not allowed to be born there – they just don’t have the facilities. Pregnant women and those on their last legs are shipped to the mainland.”

“…You have never seen Dennis Quaid like he is in this season. It’s remarkable what he’s prepared to give…”

The cinematic approach definitely enhances the drama. Dark but uplifting; that’s how Simon sees it. “There’s a lot of bereavement, loss, anger to be resolved; it’s a very emotional season which was unexpected when I started writing it,” he says. “Some of that is because of the contribution of Richard Dormer and Dennis Quaid who absolutely knocked it out the park; you have never seen Dennis Quaid like he is in this season. It’s remarkable what he’s prepared to give.”

An extended fight sequence sees Dennis’ character, topless and with his hands tied, trying to escape across the snowy expanse. Seven minutes was all he was allowed to spend in his state of undress before wardrobe were in rushed in to warm up his torso with some hardcore insulation. “There had already been minor frost-nip casualties and we quickly realised we couldn’t mess around in these conditions – life-threateningly dangerous if you didn’t do things properly,” continues Simon. “Yet in the midst of this, Dennis was rolling around on the snow, which was frozen-hard like concrete, for four or five long takes. I don’t think there are many stuntmen that would have done it. He took hold of the role by the scruff of the neck – completely committed to playing this drunkard falling apart through grief and guilt, and not hiding behind any movie-star vanity; he just went for it. I can’t think of anything I’ve seen him in where he allows himself to be as vulnerable and raw and exposed.”

“Some of the shots are just amazing – the vistas, stuff we got from helicopters and drones – but I’m not sure who’d want to go back,” agrees Drew. Least of all Dennis Quaid, we’d wager, despite his great love of the outdoors.

Meanwhile, what has become of the show’s ambiguous main man, sheriff Dan Anderssen (Richard Dormer) – having been infected by the ancient virus? “He’s evolved; he’s a new human being,” says the Irish actor after finishing an indoor scene at The Bottle Yard. “Or maybe not human… Dan is obviously not the full shilling. He’s lost his morality, but he’s stronger and wiser than ever so that’s pretty scary.”

He’s seeing interesting things, too… “He’s now addicted to muscimol juice,” Richard adds, stroking his majestic blonde moustache – four months in the making but, happily, also handy for his role as Beric Dondarrion in Game of Thrones. “It’s made from the pee of reindeer that have eaten fungi, and Eskimos or the Sami used to actually drink this to have what they thought were visions of the afterlife. So Dan has one foot in this world and the other in the land of the dead and he’s communicating with the people he’s killed.”

Dan’s already been through some extreme, sinister situations – where does a character go after they’ve crossed the line into cannibalism?

“There’s a real dichotomy to Dan and that’s what draws us back to him,” says Richard in a resonant, full-bodied voice that almost has the rest of the room reverberating. “He has to decide now. In order to survive, he’s going to have to harm others but he’s also the sheriff and his job is to look after others so it’s a terrible quandary for him and through season three we really see that struggle. Is he going to the dark side or try and save his flock and be a good shepherd?

What an exciting character to explore. “This is, without doubt, the best part I’ve ever played; and it’s my first lead in television,” Richard concurs. “There’s rarely a part where you get to grow and become something completely different yet still keep the essence of that person at the beginning. I’m really going to miss it; it’s like Dan’s my best friend. He’s a monster but I play him in the way that nobody’s truly a monster; there’s a deep humanity in him and I think that’s what makes him interesting. If he ever does anything wrong, you know it’s going to hurt him later; he has a conscience and there’s still a little seed of goodness and that’s what I hold onto. He could redeem himself…”

It’s clear the role has affected Mr Dormer deeply – he refers to the show as a Promethean creation and is visibly moved while talking about the powerful nature of the scripts as a means of personal catharsis. “It’s the Pintersque quality of the writing; what’s not said. It’s what Simon writes in between the lines which gives the actors so much room to manoeuvre. It’s been the most emotional shoot I’ve ever done and I’m really sad it’s coming to an end.

Sienna Guillory plays brilliant, blinded scientist Natalie Yelburton 

“Some characters, some souls you can relate to; in my life I’ve been through tough times and this guy is the same, trying not to lose himself. It’s a reflection of where I am and that journey of someone trying to hold onto the things he loves. It’s therapy! I feel I could play anything now because nothing could take me as far into darkness and light as this; it’s been extraordinary.”

It’s clearly been a humbling experience for all concerned. “The landscape is one of the main characters really and we’re just ants crawling around in this wilderness,” Richard continues. “Svalbard added a new dimension to the characters because we were informed by its severity and absolute brutality; it will kill you in minutes if you’re not prepared. Go 80mph on a Ski-Doo and your nose is frostbitten within seconds, if you go out for a walk you have to tell somebody because if you slip and get knocked unconscious you’re dead in 10 to 15. Everyone got tougher and meaner. Then when we did the interiors, when it was warm and cosy, out came this gentleness and love. We tried to get those extremes in the first two seasons but they really come out in this one.”

“To watch these people in this vast, Arctic, northernmost end of the world; you can’t take your eyes off of it,” agrees Dennis. “It’s a very compelling story.”

Undeniably different and joyfully alternative winter watching with elements of Greek tragedy, mysterious archaic forces and some very appealing faces in subzero cinematic wilderness – which Bristol has played a major role in creating – we don’t know about you but it’s exactly what we want to snuggle up in front of the fire with.

• Catch the show on Sky Atlantic on 6 December (Twitter: @Fortitude)