The Girl on the Train

The mystery of Megan Hipwell's disappearance unravels as Rachel Watson, piecing together fragments of a blackout night through therapy sessions with Kamal Abdic (lying about her identity to get close to him) and her own returning memories, begins to realize that her ex-husband Tom has been gaslighting her for years. Many of the drunken incidents Tom blamed her for never actually happened; he manipulated her into doubting her own sanity. As her memory clears, Rachel recalls the crucial detail: on the night Megan vanished, she saw Megan get into Tom's car.

Megan's body is eventually found. She was pregnant, and the child was fathered by neither her husband Scott nor her therapist Kamal — the two men initially suspected. Anna, Tom's current wife, separately discovers that Tom had been carrying on an affair with Megan. Armed with her restored memory and mounting suspicion, Rachel warns Anna that Tom may have killed Megan. When Anna confronts him directly, Tom confesses: he murdered Megan after she threatened to expose their affair.

Cornered, Tom turns violent, trying to beat and intimidate Rachel into silence so he won't be exposed. Rachel fights back, stabbing him with a corkscrew. Anna, rather than intervening to save him, helps ensure that Tom dies from the wound. When police arrive at the scene, Rachel and Anna support each other, corroborating their stories to present the killing as self-defense.

In the aftermath, with Tom's crimes exposed and his manipulation of her finally understood, Rachel resolves to stop drinking and rebuild her life, closing the book on the destructive cycle that had consumed her since her marriage fell apart.

The film moved the story from London to New York and kept the ending exactly.

In the novel Rachel rides the same two trains in and out of London every day, past the house on Blenheim Road where her ex-husband Tom now lives with Anna and their daughter. The film puts her on a train into New York City instead, and makes Megan the couple's former nanny.

The last stretch is the same in both. Rachel works out that Tom had been planting false memories of things she supposedly did while blacked out, remembers seeing Megan with him on the night she disappeared, and warns Anna. Cornered, Tom turns on her; Rachel gets a corkscrew into his neck and Anna finishes it, and the two women give the police matching accounts of self-defence.

The closing images differ. Harkins leaves Rachel deciding to stop drinking and move on; the film sends her to Megan's grave first, and then puts her on the train sitting on the other side of the carriage.