The Girl on the Train is a psychological thriller novel by Paula Hawkins, published in 2015. It became an international bestseller and was subsequently adapted into a 2016 film starring Emily Blunt. The book and its adaptations have captivated audiences with their suspenseful storytelling, unreliable narrators, and dark themes surrounding trauma, obsession, and deception.

The story revolves around Rachel Watson, a troubled woman who is dealing with the aftermath of a messy divorce. Rachel takes the same train every day into London, passing by a house in which she observes a seemingly perfect couple, Megan and Scott Hipwell. Rachel becomes obsessed with their life, imagining that they have the perfect marriage and life - a stark contrast to her own failing one.

However, one day, Rachel notices something unusual: Megan, the woman she’s been watching, is with another man. The next day, Megan goes missing, and Rachel, who has been drinking heavily and is often drunk during her train rides, becomes involved in the investigation, suspecting that she may have witnessed something important the night Megan disappeared. As the story unfolds, Rachel's memories begin to unravel, and she struggles to piece together what happened. Throughout the novel, multiple perspectives are presented, adding layers of mystery and suspense as Rachel, Megan, and other characters share their versions of events.