Jamie Dornan, Jemima Kirke, Lola Kirke, Ben Mendelsohn to Star in 'Untogether' (Exclusive) 

Jamie Dornan, Jemima Kirke, Lola Kirke, Ben Mendelsohn to Star in 'Untogether' (Exclusive)

From left: Jamie Dornan, Ben Mendelsohn, Jemima Kirke, Lola Kirke

Green-Light International will introduce the project this month to buyers at TIFF.

Jamie Dornan, real-life sisters Jemima Kirke (one of the stars of HBO's

follows the affair between Andrea (Jemima Kirke), a former teen prodigy turned heroin addict who is trying to be a writer now that she's sober, and Nick (Dornan), a writer who's found success with his memoir of war-time bravery, which sees him showered in wealth and women. Meanwhile, Andrea's little sister, Tara (Lola Kirke), finds her solid relationship with her older boyfriend, Martin (Mendelsohn), shaken when she is drawn to a charismatic rabbi with an even larger age gap.

Best-selling author Emma Forrest will direct the film based on her own screenplay. The project is Forrest's feature helming debut and also the first major feature film that the Kirke sisters will star in together.

Scott LaStaiti, Luke Daniels and Brandon K. Hogan will produce, while Jeff Rice will executive produce. Jeff Elliott and Chad Moore also will serve as executive producers and handle

through their sales company Green-Light International, which will be presenting it

to buyers this month at the Toronto International Film Festival. Production is slated to begin Oct. 17.

“is about the desire we all have to be seen, really seen. Sometimes we get lucky and find a partner who fulfills that criteria. Sometimes we get even luckier and meet someone who shows us that who we truly are ... is not what we’d convinced ourselves.”

with Cillian Murphy and will next star in the Netflix film

, which is set to be released in October. He also will star in the next season of crime thriller

which is launching this month on BBC and next month on Netflix. Dornan is repped by UTA, Troika in the U.K. and Sloane, Offer.

Jemima Kirke has played Jessa Johansson on HBO’s hit series

since 2012, starring opposite Lena Dunham. Her film credits include Dunham’s

. She is repped by CAA, MGMT Entertainment and Schreck Rose.

Lola Kirke's film credits include David Fincher’s

starring Tom Cruise. She has starred on the Golden Globe-winning Amazon series

since it began in 2014. The series is already slated for a third season. She is repped by ICM Partners and One Entertainment.

with Kyle Chandler. His recent film credits include

. Mendelsohn is repped by CAA, United Management and Fred Toczek.

British writer Forrest has penned several screenplays, including

All for Imagine Entertainment. She is repped by CAA and Casarotto Ramsay & Associates.