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 Girls) and Lola Kirke (who stars on Amazon’s series Mozart in the Jungle) and Ben Mendelsohn are getting together to star in indie Untogether.

Untogether 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 Untogether 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.

Forrest says Untogether “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.

Dornan is known for starring in Fifty Shades of Grey and its upcoming sequels Fifty Shades Darker and Fifty Shades Freed. He most recently starred in Anthropoid with Cillian Murphy and will next star in the Netflix film The Siege of Jadotville, which is set to be released in October. He also will star in the next season of crime thriller The Fall, 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.