Emily Blunt Was 'Wracked With Terror' Over 'The Girl on the Train,' But in a Good Way

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The film adaptation of Paula Hawkins' best-selling novel The Girl on the Train is one of the year's most anticipated movies, and no one is more cognizant of this than its star, Emily Blunt.

"I was aware there was this tsunami of interest in a book," Blunt explains in a behind-the-scenes clip. "I read it in two days, which is always an amazing sign for a thriller -- that you can't put it down."

WATCH: Emily Blunt Is Frighteningly Perfect in First 'The Girl on the Train' Trailer

The upcoming movie follows a train commuter named Rachel (Blunt) who fantasizes about a perfect couple living in a house that her train passes every day. When the woman in the couple goes missing, Rachel becomes entangled in the mystery that unfolds.

Blunt explained that the story scared her -- but in a good way -- which led her to the role.

"That's always a good sign if I'm sort of wracked with terror. It would mean I would be challenged in every way possible," Blunt says. "I could see it visually. I could see how this could work as a film. I think that's when I got really excited."

WATCH: Emily Blunt Glows on the Set of 'Girl on the Train' Following Pregnancy Announcement

If you are one of the many people who have already read the book, the movie still provides plenty of surprises. Some of the differences include setting and gender changes.

While the book is set in London, the movie takes place in New York. And instead of a male therapist, Allison Janney is the one lending a sympathetic ear to Blunt's character.

The Girl on the Train, also starring Justin Theroux, Edgar Ramirez and Lisa Kudrow, opens Oct. 7.