As we drive to the Redwater set, somewhere between Arklow and Wicklow town, there's an eerie atmosphere. The team behind the EastEnders spin-off show has remained tight-lipped as to where we're going or what the show is about. The morning mist has not yet lifted as we're shifted from one bus to another to drive down a narrow, dark dirt track to the set on Maghermore beach.

The slightly sinister feel to the drive is apt, it turns out. The spin-off centres around Kat and Alfie Moon, one of EastEnders' most notorious couples, who have found themselves a long way from Albert Square.

They left the soap in January last year in a storyline about looking for Kat’s son, who was taken from her at birth. They arrive in Ireland to Redwater, a town full of secrets.

“There was one scene in particular that we had to film on this beach at midnight and they created this mist over the sea and I thought, f*ck is this a horror film we’re making?” says Shane Richie, who plays Alfie, when we meet on set.

While it's not horror, Redwater is different from what you would expect from EastEnders. It's a drama series rather than a soap, with six hour-long episodes to explore Kat and Alfie's journey. Their story isn't unfamiliar for an Irish audience, says Jessie Wallace, who plays Kat.

"It reminds me a little bit of Philomena, it's the same concept as that. Kat wasn't aware that she had two children because when she gave birth, she'd been drinking and I think she tried to OD herself. She had tried to slit her wrists in the place where she had the baby, so she was slipping in and out of consciousness so she didn't know she had two babies. Her mum had big control over her too," she says.

"It's funnier than Philomena, I have to say that," adds Fionnula Flanagan when she joins. The Lost star is one of many Irish actors to join the impressive ensemble cast that includes Maria Doyle Kennedy (Orphan Black), Angeline Ball (Shameless), Ian McElhinney (Game of Thrones) and Peter Campion (Brooklyn).

Danish director

"This is Irish noir. We call it dubh," says Flanagan, referring to the influence Borgen director Jasper Nielsen has had on production. "It was very interesting to have a Danish director for four of the episodes, and the perspective that he brought. He really is a film director, he has a film approach to things and he's kind of playful. He gave us a lot of leeway to play."

Flanagan plays Agnes, essentially the matriarch of the town of Redwater, acting as the keeper of its secrets. She doesn’t take well to the arrival of Kat and Alfie, who she views as poking around in her town and her family’s business.

“Oh my god, I wonder why this woman hasn’t been murdered long ago,” says Flanagan. “I said it after one take the other day, how hasn’t someone murdered her? I would. She’s very manipulative so that’s what makes it yummy to play. Who wants to be nice? This is much more interesting.”

Doyle Kennedy plays Róisín, one of Agnes’ two daughters, alongside Eileen, played by Ball. The whole family is involved with Kat’s child, who is a part of the Redwater town and who Doyle Kennedy says “has impacted on all of our lives”. While the story has some resonance here given Ireland’s history, she says the show should have broad appeal.

“It’s universal in the way that it’s about a family and about secrets. What family doesn’t have a few? The damage that information that’s repressed does, and it never stays buried, it never stays hidden. It comes to the surface eventually and you have to deal with that,” she says.

"There's senses of The Wicker Man in it. They don't let outsiders in," says Ball. "Obviously it's set now and it's modern but there is an old sense of guardedness. You've got this dark undercurrent, which I think is great because people just don't want to see twee anymore."

Different pace

Shooting a drama has been a treat for Wallace and Richie, who are used to shooting up to 25 scenes a day for EastEnders, compared to five or less on Redwater.

"With EastEnders, it's fast food, it's got to be one line or one sentence or one look. We got a chance [with Redwater] to embellish the stories, and with the writing as well was incredible. There's something about doing it on single camera as well," says Richie

"The pace is completely different," adds Wallace. "It's not a different type of acting, it's more like a habit you fall into when you work in EastEnders where the pace is much quicker. There's a lot of shouting and you've got to do everything quick. Whereas here, I've had to pull it back, it's much calmer really."

Soap fans might notice a change in the couple in Redwater. Kat in particular has lost the brassy east end look and some of the edge people associate with her character.

“I’ve found another layer to Kat,” says Wallace. “She has changed. Even the way she dresses has changed. I’ve got all these extensions. She’s become very bohemian but there are still elements of the hardness of Kat. That’s still there but I’ve tried to change her.”

Alfie has also softened around the edges, his battle with a brain tumour only really playing out in this show. “For the first time in 15 years of playing Alfie, he questions himself as a father, a husband and as a life, it feels like it’s coming to an end for him,” says Richie.

“Alfie starts getting hallucinations and one in particular is quite harrowing. It’s very religious as well, for some reason. I don’t know how much I can say… We tap into religion in quite a big way, something that I didn’t think the writers at the BBC would have the balls to do. They certainly have done, they’ve taken that full on and it’s quite evident in the writing and the way it’s being played as well,” he says.

New audience

Ball starred in a few episodes of EastEnders years ago, but not at the same time that Richie and Wallace were working on the show. Doyle Kennedy and Flanagan come to the show completely fresh.

"I'd never seen EastEnders until I met the two of them [Wallace and Richie], and then I thought, I better take a look at this programme," says Flanagan, laughing. "I only saw one episode... I didn't know anybody. Everyone was fighting a lot, everyone on screen was fighting, screaming, yelling, divorcing, stabbing, murdering. Everything was going on."

While Richie feels the EastEnders audience will be satisified with Kat and Alfie's new venture, he says Redwater is making space for a new audience at the end of the day.

"If you've never seen it [EastEnders] before, it won't matter because the story has been beautifully told, so in episode one, you know straight away who Kat and Alfie are, what their journey is, what their backstory is, even if you've never seen EastEnders… There's a whole audience who watch Happy Valley, Doctor Foster, Broadchurch, that might not necessarily watch EastEnders, but they'll get this."

Redwater airs on RTÉ One and BBC One on Sunday, May 14th at 9.30pm