Emily Blunt and Rebecca Ferguson will star in the upcoming film The Girl On the Train. The film is based on the best-selling book of the same name, written by Paula Hawkins.

Blunt is set to play the film’s lead–Rachel. Rachel is an unemployed alcoholic–divorced from her husband because of her drinking problems. Rebecca Ferguson will play the ex-husband’s new wife, Anna.

Emily Blunt’s character narrates the novel. It is, of course, uncertain if she will serve as narrator in the film, but it will require a significant story line change if that doesn’t happen. Rachel spends a great deal of time on the train. She has caught glimpses of a young couple she passes during her daily train ride, and obsesses over the seemingly idyllic life they live. Rachel’s roommate thinks she is working–and later looking for a job–when she leaves on the train each day, but she has long since lost her job.

Find out who will be joining Emily Blunt in 'The Girl on the Train': http://t.co/aU3zQIK1zF pic.twitter.com/6pRIeIe5eK

— JustJared.com (@JustJared) August 20, 2015

Upon returning from one such ride on the train–and a drunken blackout–covered in blood, Rachel has no idea what happened to her. She fears, however, that she may have been involved in a crime.

Emily Blunt will no doubt shine in this compelling role, but Rebecca Ferguson’s role will likely be almost as intriguing.

Rebecca Ferguson joins The Girl On the Train cast opposite Emily Blunt | Daily Mail Online http://t.co/sJ4iFloDUK

— Publishers Weekly (@PublishersWkly) August 19, 2015

The Girl on the Train is the fastest-selling adult novel in history. It has sold more than two million copies in the U.S. alone since it was published back in January by Riverhead Books. It hit the top spot on the New York Times best sellers list in its first week of eligibility.

Casting is still taking place, so production has yet to begin. Will you be checking out Emily Blunt and Rebecca Ferguson in The Girl On the Train when it hits theaters?