Joanne Froggatt has joined the cast of 'The Secrets'.
The 'Downton Abbey' actress will star alongside Ben Chaplin and 'Silent Witness' star Emilia Fox in an episode of the new drama series, which is made up of five standalone films that have been commissioned to support new writing talent.
The 33-year-old actress will appear in the first instalment of 'The Secrets' - made by Working Title TV for BBC One - which was written by Elinor Cook and tells the story of a man who is married to two women and is living a secret double life. However, his cheating is eventually exposed and the drama aims to explore whether monogamy is a realistic proposition.
All five films will be directed by BAFTA Award winner Dominic Savage, who also co-wrote the fourth episode with up-and-coming writer Nick Payne.
Nick also wrote the second episode, while the remaining two films were written by Sarah Solemani and Ben Ockrent.
Working Title's Juliette Howell said: "I'm thrilled Dominic has assembled such a stellar line up. It's hugely exciting to see so many of our finest actors bringing these original distinctive new voices to life on BBC One."

Cara Delevingne will make her TV acting debut in a Sky Arts one-off drama.
The 21-year-old model - who has recently turned her hand to film work - will be one of the stars featured in the latest 'Playhouse Presents...' strand, starring in 'Timeless'.
The drama follows Chloe (Cara) and her great-grandmother Alice (Sylvia Syms), who, despite their generational gap, bond over their shared "pain of having been separated from their partners by war".
Chloe's fiancé is currently serving in Afghanistan and when an army official arrives on her doorstep, a shocking revelation will stir emotions in both characters.
The latest 'Playhouse Presents...' strand will also mark 'Friends' actor Matthew Perry's first British acting role, as he stars in a comedy titled 'The Dog Thrower', about a man who gains fame by performing tricks with his pet pup.
Other actors who will feature in one-off dramas and comedies to air as part of the strand include Billie Piper, Ben Whishaw, Mark Strong, Ashley Walters and Richard Wilson.
Sky Arts director James Hunt said: "What a phenomenal line-up for this year's 'Playhouse Presents...' Sky Arts has built on its huge success in comedy and drama over the past two years. We're delighted that such outstanding writers, directors and actors, all at the very top of their game, want to come and 'play' with us."
'Playhouse Presents...' begins with 'The Dog Thrower' on May 1 and ends with 'Timeless' on June 19.

Kerry Katona says her latest pregnancy has been her best yet.
The former Atomic Kitten singer - who is already mother to Molly, 12, and Lilly Sue, 11, with first husband Brian McFadden and Heidi, seven, and Max, five, with second husband Mark Croft - is relieved that her fifth pregnancy has been smooth sailing and credits fiancé George Kay for making her feel so relaxed.
She said: "This is the best pregnancy I've ever had. I think it's because I'm happy. George is a great support and I'm genuinely in love."
Kerry, 33, also expressed her delight that she hasn't gained as much weight this time.
She gushed: "I'm all belly and bump and I'm the smallest I've ever been. I'm 11 stone and I'm usually nine, so I've only put on two stone. With Max I put on four! It'll only take me about a month to lose the weight. As soon as I get my mind set on something, it just falls off me."
'The Big Reunion' star - who filed for bankruptcy a second time last year - hit back at claims she has been renting a £5,000 home for her family.
She told Britain's OK! magazine: "I'm not saying how much my rent is, but I'm following the right procedures. Do you honestly think my trustees would let me spend £5,000 on a house? The mansion in Wilmslow [in Chesire, England] was only £3,200. Put it this way, this is cheaper than that one."

NeNe Leakes will compete on 'Dancing With The Stars'.
The outspoken 'Real Housewives of Atlanta' star is set to join the likes of 'Price Is Right' host Drew Carey, former ice hockey player Sean Avery and 'Full House' alumni Candace Cameron Bure on the 18th season of the popular ballroom dancing show.
The full line-up was officially unveiled on 'Good Morning America' this morning (04.03.14) and features a heavy dose of athletes.
Double-amputee snowboarding champion Amy Purdy, who will be partnered with professional dancer Derek Hough, long-distance swimmer Diana Nyad, and Olympic figure skaters Charlie White and Meryl Davis have all signed on to compete.
The cast is rounded out by the 'Wonder Years' star Danica McKellar, actor Billy Dee Williams, Big Time Rush singer James Maslow and Australian pop singer Cody Simpson.
This year co-host Brooke Burke-Charvet is being replaced by former contestant Erin Andrews and dancing professional Maksim Chmerkovskiy will be rejoining the programme.
Brooke good-humouredly joked about her dismissal along with musical director Rob Wheeler and his 28-strong backing band's last month.
She wrote on Twitter: "So much chatter bout DWTS. I'm really cool, everyoneI did my 7 seasons, had a blast! I'm ready for change. I love your loyalty. Thank you!
"Here's the skinny - the show found out Harold Wheeler, the band, Rob & me were putting together our own road show, so they fired us all! (sic)"
'Dancing With The Stars' kicks off on March 17 on ABC.

Cameron Diaz is a "science nerd".
The 41-year-old actress has recently been working on 'The Body Book' and says she was inspired to write the tome because of her fascination with how things work.
She said: "I'm a science nerd. I like to know why things work the way they do. I thought that the body was probably the most important thing to understand how it works since we all have one, and we don't really know that much about it."
The 'Bad Teacher' star also urged women to take better care of their private parts and treat their genitals like "beautiful flowers".
Speaking on 'Chelsea Lately', she said: "We think the vagina is on the outside. I say grab a mirror and play along. Get in there.
"Learn about it. You're supposed to treat it like the beautiful flower that is, the delicate flower that it is. And you're supposed to nurture it in all the ways that it needs nurturing. Watering it. Fertilising it. It needs nourishment. It's hungry."
And Cameron also called women not to permanently remove their pubic hair.
Explaining why she included an excerpt about pubic hair preservation, she said: "Because it's a science book, and since we used to be covered in hair, and now we're not except for a few places, I figure there's a purpose for that hair.
"So I put some of the purposes for it and I also suggest that no mater how you enjoy grooming it throughout your life - whether it's shave it all off, wax it all off, putt a bulls eye, birthday cake, I don't care - just, girls, think about not taking it all off forever. Permanency means forever. It doesn't come back. You might change your mind in a few years."

Jessica Alba buys her furniture from second-hand websites.
The 32-year-old actress - who has daughters Honor, five, and two-year-old Haven with husband Cash Warren - admits she has a "problem" and can't stop splashing out on items advertised on Craislist.
She said: "I bought my hot pink desk off Craigslist. I have a problem. I love vintage furniture, and refurbishing is one of the most eco things you can do. I also got a couple of cool chairs and Danish mid-century credenzas off of Craigslist."
And the sales site isn't the only reason Jessica goes online, as she is also "addicted" to photo-sharing website Instagram.
She told the new issue of Redbook magazine: "All [Cash] watches is sports. Fantasy football is so annoying--there's always a game on. Though he says I'm addicted to Instagram, so it goes both ways!"
Away from the spotlight, the 'Sin City: A Dame to Kill For' is closer to her friends from her baby group than anyone, though her presence can sometimes make hanging out difficult.
She explained: "They're some of my closest girlfriends. It's weird when we're doing normal mom things and there's paparazzi around. That's the only thing that makes everyone uncomfortable."

Khloe Kardashian and Lamar Odom's former marital home in Tarzana has been burgled. The crime was discovered on Monday night (03.03.14) when the reality TV star was with her mother and manager, Kris Jenner, clearing out the Los Angeles mansion which sh...

Margot Robbie failed to raise a smile as she arrived at LAX Airport. 'The Wolf Of Wall Street' star looked stylish in oversize shades and a classic trench coat.

Reese Witherspoon looked stunning in a cleavage baring top as she left the AGO after Oscars party in LA. The 'Legally Blonde' actress finished off her look with a sequinned pencil skirt and sophisticated black jacket.

Paris Hilton looked ready for spring as she grabbed a lemonade to go in Beverly Hills. The heiress teamed her white jeans and sweater with a matching handbag and shades.

Jessica Alba wrapped up warm in a striped overcoat as she landed in New York. Unfortunately the 'Sin City' actress still looked a little chilly as she clutched a shopping bag outside JFK Airport.

Rihanna clashed her green hooded jacket with red vintage-inspired shades as she hit the Stella McCartney Autumn/Winter 2014-15 fashion show at the Paris Opera House.