Here’s a concise plot recap for The Girl on the Train (2016):
Rachel Watson, a recovering alcoholic reeling from her divorce and infertility, spends her daily train commutes obsessing over a seemingly perfect couple, Megan and Scott Hipwell, who live in a neighborhood she passes through every day. Rachel also fixates on her ex-husband Tom and his new wife, Anna, who now live in Rachel’s old home.
One day from the train, Rachel sees Megan in a compromising setting with a man who isn’t her husband. After drinking heavily, she tries to confront Megan but blacks out. The next morning she wakes up injured and can't remember what happened. Soon, Megan goes missing.
The investigation casts suspicion on several people: Megan’s husband Scott, her psychiatrist Dr. Abdic, and even Rachel herself due to her unreliability and frequent blackouts. As Rachel digs for answers, she starts uncovering hidden truths—not just about Megan but about her own past.
Eventually, Rachel pieces together that Tom had an affair with Megan and, feeling threatened when she became pregnant with his child, went as far as killing her. In the climax, Rachel and Anna confront Tom; in self-defense, Rachel fatally stabs him. Both women later tell the police that Rachel’s actions were justified after Tom admits to being Megan’s killer. Rachel ends the story sober, leaving her old life behind and sitting on the opposite side of the train—symbolizing a fresh start.
If you want a look at how the film differs from the book, I can pull that up too.
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