Rachel Watson (Blunt) commutes to Manhattan every day, longing to have the life of those who live in the wonderful houses outside her window. In particular Megan's (Bennett), whose marriage to the buff Scott (Luke Evans) looks like the perfect one. But it turns out Rachel did have this life and a house like this: two years ago she lived two doors down with Tom (Theroux) until they split post his affair with Anna (Ferguson), his current wife and with whom he has a baby. When Megan, who is a nanny for Anna and Tom, goes missing Rachel, posing as Megan's friend, approaches Scott with some delicate information as to her whereabouts.

Although the script has moved Paula Hawkins' novel from London to New York, trimming one of its narrators in the process (Anna's point of view is reduced somewhat), Erin Cressida Wilson's (writer of Secretary, Chloe, and Men, Women and Children) adaptation holds fast to the novel's themes of memory and the effects of emotional abuse. It's a real writer's screenplay, heavy on character backstory and nuance, but regardless of the detailed characterisations The Girl On The Train is a mystery first and foremost and a cracking one at that.

Because the story has no clear point of view and the protagonists can't be trusted the mystery is built on shifting sands. Boasting not one but two unreliable narrators, important new information on Rachel and Megan is slipped out make one doubt what has been said and seen. Rachel is an alcoholic who is prone to bizarre behaviour during blackouts, and Wilson's script delights in making one question that what she sees or experiences is in fact real; what is accepted as fact can suddenly become questionable.

Moving from her fairy tale view of Megan's life ("she’s everything I lost, she's everything I want to be," she says at one point), we get a different version once inside Megan's head. She feels trapped, Scott pushing her to have a baby she doesn't want. But Megan is severely depressed, still haunted by a tragedy in her youth, and seems to be toying with psychiatrist (Edgar Ramirez, Point Break remake). In an addition to that there are short, stabbing flashbacks that can either fill the audience in on essential backstory or give them a distorted view of what has happened in the lead up to Megan's disappearance. What to believe? Nobody here is clean. Everyone is a suspect.

While the last ten minutes get a bit wonky, the impeccable performances hold things together. Blunt has never been better. The desperation, the loneliness, the struggle with alcoholism, the anger at a life stolen – it's all there in her red eyes.