Meet Rachel Watson, the unreliable narrator who has galvanized readers since Paula Hawkins’ “The Girl on the Train” was released in 2015. Rachel and her suspenseful, sordid tale are headed to the big-screen in an upcoming adaptation of the best-selling book, for which the first trailer has just dropped.

Emily Blunt (“Sicario”) takes on the role of Rachel, an alcoholic woman whose life is in shambles. Rachel becomes fixated on the disappearance of a woman (Hayley Bennett, “The Equalizer”) her ex-husband (Justin Theroux, “The Leftovers”) employed as a nanny. It’s not long before Rachel becomes a suspect in the crime.

Rachel has witnessed something she can’t forget — but she can’t quite remember it either. She holds the keys to the mystery but her lapses in memory make it impossible for her to make sense of what’s happened.

“I’m afraid of myself,” Rachel tearfully admits in the spot for the film. Blunt has said that taking on the role was “the most challenging thing [she’s] ever done.”

Check out the tense, atmospheric trailer below. “The Girl on the Train” opens October 7. The script was penned by Erin Cressida Wilson (“Men, Women & Children”). You can catch Blunt in theaters on Friday in “The Huntsman: Winter’s War.”