Emily Blunt's role in 'The Girl on the Train' is the most "challenging" part she's undertaken.
The British actress portrays troubled divorcee Rachel Watson in the thriller and found the part very "exposing and emotional".
She said: "It's the most challenging role I've ever been asked to do, and the role that requires all of me. Very exposing, very exciting work.
"It's working in a very emotional way. It's not a walk in the park, in any capacity."
The movie - which is based on Paula Hawkins' debut novel - explores the disappearance of the seemingly-perfect Megan (Haley Bennett) but Emily insists the most interesting part of the movie isn't the whodunnit aspect.
She said: "Yes there is a thriller element but that was never the aspect of the book I found the most exciting - 'Who murdered who?'
"It was actually this great portrayal of three incredibly damaged women, particularly my character, and it's about addiction and it's about voyeurism and what we think we see and don't see."
Emily's character has no memory of her movements on the night of Megan's disappearance and found her storyline "really exciting".
She said: "The fact that your heroine is a blackout drunk is really exciting - she becomes the most unreliable witness and spends the whole film trying to remember what she saw because she was drunk. And I think it's a thrilling way to work."