Eve Myles returns to screens tonight in the first episode of gripping drama Keeping Faith.

The Torchwood actress plays lawyer, wife and mother Faith Howells, whose life is turned upside down when her husband and business partner Evan mysteriously disappears.

The series presented Myles with a unique challenge – filmed simultaneously in English and Welsh, Keeping Faith required her to learn a new language from scratch.

"I was at home, quite heavily pregnant," Myles tells Digital Spy. "Pip [Broughton, director] and I had a relationship. We'd worked together before. She phoned me up and said, 'There's a script we've been working on for a couple of years. You must play the part.'

BBC Wales

"I couldn't believe how lucky I was. Then she said it was being filmed back to back, in Welsh and English. And I kind of thought, 'Do I break the news now, or do I try to convince them not to do it in Welsh, because then I can play the part?'

"I thought, 'Just be bold.' I said, 'It would be lovely, but I don't speak Welsh.'

"She said, 'Well, would you mind [learning]?' I went, 'No, no, I can't. I have two children. How do you do that at 38?' So she said, 'I'll send you the script anyway. I'd like to see what you'd think of it'."

According to Myles, the script – by Matthew Hall – was "wonderful", while the formidable task of learning Welsh was "the kick [she] needed" after becoming "disillusioned" with acting.

"I'd just been on Broadchurch, actually, and that was great, but at that point, I was quite disillusioned actually with the business and my job. I kept turning down work because I found it disinteresting. I had nothing in me, to be honest. I was a bit passionless.

"I was trying to sign up to train as a midwife! I haven't told anyone that. My husband knows!

"So yeah, I was considering a big change, because... I don't know. I was finding it all a little same-y. I thought, 'Maybe I was very unhappy with work. Maybe I need a change.'

BBC Wales

"So I considered [quitting]. I'm the type of character who likes to be challenged, and I wasn't being challenged. Then this came through, and I thought, 'What bigger challenge would I have?'

"Even if this job was just in English, it would have been a huge challenge to play Faith Howells. Already, it was huge – and it was in two languages.

"I thought to myself, 'In five years' time, if I look back at this, and somebody else played this part and I didn't give it a go, I'm going to be desperately unhappy with myself. I don't know if I can live with that. Because I know this is a good piece.'

"So I took the challenge. It was live, breathe and die – every single day on the show. But it was the kick I needed, and it was the challenge I needed. And I've never loved my job so much."

The Welsh-language version of Keeping Faith has already aired on S4C, under the title of Un Bore Mercher, with the series – and in particular Myles's performance – earning strong reviews.

"The love and the support was just mind-blowing," she says. "I think it's... I don't know. If you're put on the edge of a cliff, you're going to surprise yourself. And that's kind of what happened."

Keeping Faith begins tonight at 9pm on BBC One.

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