Laura Prepon Joins 'The Girl On The Train,' But Who Will She Be Playing?

If you got hooked on the mystery of Gone Girl, then you should get hyped for the upcoming adaptation of another twisted bestseller. ICYMI, Paula Hawkins' novel The Girl On The Train is getting the big screen treatment, and now the cast is rounding out. While it was already known that Emily Blunt will star as Rachel, an alcoholic who thrusts herself into a missing person's case, and that Allison Janney, Justin Thereoux, and Jared Leto will all have roles in the upcoming thriller, the latest person to join the movie is a small screen favorite. Orange Is The New Black's Laura Prepon has joined the cast of The Girl On The Train , and it might make you miss Alex Vause just a little bit less.

According to Deadline, Prepon will be playing Cathy, the roommate of Blunt's character, Rachel. In Hawkins' original novel, Cathy is a woman that Rachel was friendly with in college who becomes her roommate when Rachel's marriage falls apart. In the novel, Cathy is English and lives in the outskirts of London, but according to Entertainment Weekly, this setting will have changed for the upcoming film. As Entertainment Weekly reports, the girl on the train won't be commuting to London — though Rachel will remain a Brit, her daily destination will be Manhattan. This means that Prepon could likely be playing a New Yorker (or, perhaps, a New Jersey resident living in the 'burbs) rather than an English woman.

Prepon will certainly have a lot to play off of in the new film, should it follow the story of the novel. As the roommate of the troubled Rachel, it's Cathy who has to pick Rachel off the floor after another drunken evening and make sure that she comes home safe. Still, Cathy is also one of the characters most in the dark about Rachel's true self: Though Rachel does take the train every day, in the book she has lost her job and commutes into the city just to keep up appearances for Cathy and the rest of the world.

I'm already super stoked for this adaptation (I basically glued Hawkins' book to my hands, because that's how much I didn't want to put it down) and now that the cast is filling out, we can all finally get a clear picture of how the film will look. Unfortunately, tidbits of info will be all we have to go on for a while: The upcoming film won't hit theaters until Oct. 7, 2016. Here's hoping that the wait goes by as quickly as reading the book did.