The trailer for The Pact starts with a group of laughing women, stumbling with their torches through a dark wood at night - where we later learn a body has been found.

It is a very spooky-looking location, which plays a huge part in the first episode of the BBC One drama.

And if you are wondering whether it's challenging to film the scenes there, you would be right.

"It was a nightmare, and it went on forever," admits Scottish star Laura Fraser, 45.

"We had to keep going back and reshooting, because the weather was sublime for the entire shoot, apart from when we went and did all the exterior shots in the woods. And it was like hell on earth. It was chucking it down, freezing.

"We were always laughing [on set], but I don't think we laughed in the woods."

Cinematic, intriguing, and powerfully acted by some big names in TV, the new six-part series, which was made in Wales, follows a group of work friends in the aftermath of the sudden death of their young brewery boss.

Bound by a secret that will change their lives forever, they are drawn into a fragile pact of silence - but can they all cope with the web of lies that is forming?

Here, Fraser, plus her co-stars Julie Hesmondhalgh and Rakie Ayola, reveal more about what viewers can expect.

COMPLEX ROLES

Fraser - known for Breaking Bad, Traces and Better Call Saul - plays Anna, who is not in agreement with the pact, but goes along with it anyway.

We see not only her friendships put under extreme pressure but also her marriage; her husband Max (Jason Hughes) is a police officer investigating the shocking death while being completely unaware that his wife is linked to the case.

"Their lives are changed forever," reflects Fraser.

"Things start to spiral out of control, and I'm very interested in things spiralling out of control and exploring living in constant fear. I found that all very interesting."

Hesmondhalgh, 51 - best known for playing Hayley Cropper in Coronation Street - portrays Nancy, who is "the driving force behind not going to the police and forming this pact".

"The deeper reasons for that unfold as the series progresses," teases the Lancashire-born actress, who has also starred in Broadchurch and The A Word.

"I felt she was quite different from me, in that she's a little bit more buttoned-up than I am, and she's the mum of the group."

Leading the investigation into this "strange murder" is Detective Superintendent Holland, played by Noughts & Crosses star Rakie Ayola.

The 52-year-old liked how much depth writer Peter McTighe (known for Doctor Who) had given to her character, noting it was different from other scripts because, "in a story like this, the investigating officers can often be procedural and not much more, so they're not particularly interesting".

WELSH WONDERS

One of the reasons The Pact is so captivating is the stunningly picturesque scenery.

Filming locations included Merthyr Tydfil, which was eye-opening for Ayola, who hails from Cardiff, and also recently starred in ITV drama Grace.

"Every time I was on set, I was just saying out loud, 'Why have I never come in this direction from Cardiff?' I'd never gone north for an hour. So, it was like a different country to me, and it made me quite sad I'd never gone there before. So beautiful."

The stars have also discussed how they shot scenes in Pontsticill, Rhymney Brewery, and Usk.

"It felt like a massive privilege to be able to be working during the pandemic, and also working in such a beautiful place," enthuses cheery Hesmondhalgh.

"We were based in Cardiff, which is a city I absolutely have fallen in love with completely. But all the different places we went to and filmed were just astonishing.

"It was a really amazing experience and, like all experiences, it sometimes takes you stepping away to realise how lucky you were to do it, because when you're working, you're just in it and doing it."

FEMALE FRIENDSHIP

Unpacking the themes of the drama, Ayola discusses how nuanced McTighe's approach is to the story.

"I don't know if you had a story about a group of men and they were friends, that you would take the time to just let them see how they are with each other," she says of the fact it is women at the forefront of the series.

"There would always be somebody else to fight, somebody else to punch, somebody else to throw a chair at.

"This is just a group of mates, and it's really lovely. And it's unusual because it's not, 'You stole my husband, what are we going to do about it?' - which is usually what happens when it's a group of women - 'Give me my man back!'

"It's 'I need your help. You need my help. How can we work together?' It's very grown-up in that respect.

LOCKDOWN LIFE

Fraser does not shy away from admitting she found it tricky filming with Covid-19 restrictions in place.

"It became a little bit easier, but it never felt natural," she recalls.

"And in general, it was hard because I got home once in four months for four days, and my family couldn't visit me, because I live in Glasgow, and the various different tiers and restrictions meant that it was quite lonely in that respect.

"But the cast and crew were so full of love, and we really did have a little family going for the shoot."

Another role Hesmondhalgh has had during the pandemic has been making videos of herself to cheer people up; she has been sending messages to exhausted NHS workers, as well as recording stories for children's charities.

"It's nice to feel like you're doing something, even though it feels deeply mortifying that's all you can do during these times," she reflects.

"But I do feel something that has come out of the pandemic - in terms of our profession - is that people have really needed entertainment, people have needed good storytelling and art - whether that's music or films or TV or radio.

"And in terms of young people who might be thinking of joining the profession, who've been told constantly that it's just a bit of fluff and nothing to be proud of and not a proper job, I hope it's encouraged people to see just how central to people's lives the arts are."

The Pact, BBC1, Monday/Tuesday at 9pm