Every morning and evening, Rachel Watson (Emily Blunt) commutes to and from the city by train, getting lost in the lives of the people whose idyllic suburban New York homes she passes. Her favorite couple: Megan (Haley Bennett) and Scott Hipwell (Luke Evans), who appear from the outside to have the kind of perfect romance she wasn't able to hold onto with ex-husband Tom (Justin Theroux). This fantasy is a fleeting respite to her troubled, aimless reality of alcoholism and unemployment. And then, one day, she sees something she can't unsee—a betrayal that leads to a missing person and fears that her blackout may hold the key to an unthinkable crime.

Based on Paula Hawkins' best-selling 2015 mystery novel, "The Girl on the Train" has received a mostly faithful if somewhat less penetrating big-screen adaptation from director Tate Taylor (2011's "The Help") and screenwriter Erin Cressida Wilson (2014's "Men, Women & Children"). One smartly retained device is the revolving-door narrative, moving from present to past and back again as it follows three women: Rachel, still struggling to move on after the dissolution of her marriage; Megan, whose life isn't at all what Rachel presumes from her daily eavesdropping perspective; and Anna (Rebecca Ferguson), Tom's mistress-turned-new-wife who promptly moved into Rachel's old home and had the baby she couldn't give him. If the storytelling structure is rock-solid, meticulously dropping breadcrumbs throughout which bring insight into these wounded people, the screenplay still does not delve as deeply into their day-to-day thoughts and routines as one hopes. Anna, for example, remains something of a cipher, while the self-destructive Megan is so fascinating it is a shame to not get a clear feel for her relationship with Scott and the psychology behind the self-destructive actions she has long been making behind his back.

The picture's biggest success is the treatment of the third and most prominent point of view. Rachel is not the kind of protagonist normally seen in studio filmmaking, and this is a very good thing. She's lost and confused, a shadow of her former self wandering in an abyss of booze and shattered dreams. Having lost her job a year ago, she hides the truth from roommate and landlord Cathy (Laura Prepon) by heading into Manhattan each morning, biding her time in parks and at bars. She is fairly certain she doesn't mean ill of anyone, but also cannot trust herself when she drinks too much and her memory goes fuzzy. It is this pattern—continuing to send unanswered calls to Tom, being accused of attempting to abduct his and Anna's baby—which haunts Rachel, the consequences only growing more potentially dire when she wakes from her latest blackout with a bloody head wound on the same day news spreads of Megan's vanishing.

Emily Blunt (2015's "Sicario") is stunning in the role of Rachel, digging deeply and affectingly into the sloshy mind frame of someone who cannot begin to fix herself until she uncovers the truth about the fateful missing night in question. The plot she is in is scrupulously designed if decidedly pulpy, its rather predictable trajectory never quite matching the excellence of Blunt and the stark guilelessness of her character. As Megan, Haley Bennett (2016's "Hardcore Henry") expertly navigates a difficult part, making the most of what feels more like snapshots rather than a three-dimensional study of who she is. Rebecca Ferguson (2016's "Florence Foster Jenkins"), who has proven chameleonic in her wildly different roles since her breakthrough in 2015's "Mission: Impossible — Rogue Nation," softens Anna ever so slightly from the book, giving more sympathetic shades to an insecure woman still adjusting to motherhood.

The supporting cast—including Justin Theroux (2012's "Wanderlust") as Rachel's unfaithful ex-husband Tom; Luke Evans (2015's "Furious 7") as Megan's husband Scott, with whom Rachel strikes up an unexpected friendship; Édgar Ramírez (2014's "Deliver Us from Evil") as Megan's therapist and potential suspect Dr. Kamal Abdic; Allison Janney (2016's "Miss Peregrine's Home for Peculiar Children") as by-the-book Detective Riley; and Lisa Kudrow (2016's "Neighbors 2: Sorority Rising"), giving memorable spark to her limited screen time as Martha, an acquaintance from Rachel's past—is close to faultless even as the actors often seem to be trapped by the restricted confines of the twisty, purposefully unforthcoming script.

"The Girl on the Train" is a sudsy potboiler with an enticingly gritty, largely uncompromised lead character. Director Tate Taylor has transplanted the story from London to New York while, notably, keeping Blunt's British accent—all the better to suggest her sense of displacement. The indelible locations used in and around the Westchester burg of Ardsley-on-Hudson leap off the screen, moodily suggesting the dark underbelly of picture-postcard surroundings. While the film does not add up to as much as the setup might suggest, the getting-there is captivating enough to smooth over its rougher edges. Standing like a beacon at its center is Emily Blunt, capturing the aching authenticity of a distraught soul in search of answers and solace.