Should all go well in London, the production, which will be directed by Ian Rickson, will arrive on Broadway in fall 2011, according to the New York Times. Any earlier transfer is not possible due to the filming demands of both actresses.

Both the London and Broadway mountings will be produced by Sonia Friedman Productions and Scott Landis, who are also responsible for the current Broadway revival of La Bete, another London-to-Broadway transfer.

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Moss, who will make her West End debut in The Children's Hour, is best known for playing the role of Peggy Olson in the award-winning television series "Mad Men," for which she has received both Emmy Award and SAG Award nominations, as well as for the role of Zoe Bartlett in "The West Wing." She made her Broadway stage debut in David Mamet's Speed the Plow in 2008. Film credits include "Get Him to the Greek," "Did you Hear About the Morgans?" and "Girl, Interrupted," as well as the forthcoming "On the Road" and "Darling Companion."

Knightley previously appeared on the West End stage in The Misanthrope that opened in December 2009 at the Comedy Theatre, running through March 2010. She is best known for her film appearances in "Bend It Like Beckham," "Atonement" with James McAvoy, "The Duchess," "The Edge Of Love" with Sienna Miller, "Domino," "The Jacket," "Pride And Prejudice" (for which she was Oscar-nominated), as the feisty Elizabeth Swann in the "Pirates of the Caribbean" movies, and in the recently released "Never Let Me Go" (which opened this year's London Film Festival). She will also be seen in the forthcoming "London Boulevard" and "A Dangerous Method." In Hellman's play, originally premiered on Broadway in 1934, a troubled teenager starts to spin a web of deceit and all around her are soon caught up in it. It was last seen in London when Howard Davies directed it at the National Theatre with a cast that included Clare Higgins, Harriet Walter and Emily Watson. Karen Wright (Knightley) and Martha Dobie (Moss) have worked for years to establish their all-girls boarding school, and now, with the school flourishing and Karen on the verge of marriage, their lives and loves finally appear secure. However, when malicious student Mary runs away from the school and seeks to avoid being sent back, she draws on hearsay, gossip, and her own imagination, to concoct a story that threatens the school, the marriage, and their entire futures.

Rickson was last represented in London by his production of Jerusalem that transferred from the Royal Court to the West End's Apollo Theatre. Previous productions for the Royal Court, where he was artistic director from 1998 to 2006, include The Seagull (subsequently transferring to Broadway, with Kristin Scott Thomas), Krapp's Last Tape (with Harold Pinter), Mouth to Mouth (also West End) and The Weir (also West End and Broadway). Other credits since leaving the Royal Court include directing Parlour Song (Almeida), The Hothouse (National Theatre), Hedda Gabler (Roundabout Theatre Company, New York) and screen adaptations of "Fallout" and "Krapp's Last Tape."