Rachel Watson, an unemployed alcoholic, rides the same commuter train every day, passing by the neighborhood where her ex-husband, Tom, lives with his new wife, Anna, and their baby. The routine provides her a strange solace, and she becomes fixated on a seemingly perfect couple, Scott and Megan Hipwell, whom she observes from the train window. Their love appears idyllic compared to her shattered life, and she fantasizes about their relationship, giving them imaginary names and lives. However, one day, Rachel sees something shocking from the train—Megan in the arms of another man. Soon after, Megan disappears, and Rachel, plagued by blackouts and unreliable memories due to her drinking, becomes determined to uncover the truth.

As Rachel investigates Megan’s disappearance, she inserts herself into Scott’s life, pretending to have known Megan. Scott, desperate for answers, welcomes Rachel’s support, unaware of her personal struggles. Meanwhile, Anna grows increasingly concerned about Rachel’s presence, fearing for the safety of her family. Rachel’s attempts to recall the night Megan vanished are hindered by her alcohol-induced memory gaps, but she slowly starts piecing together fragmented recollections. Megan’s own past is gradually unveiled, revealing a tragic history of loss, infidelity, and emotional turmoil. She had been having an affair with her therapist, Dr. Kamal Abdic, further complicating the case.

As the police begin suspecting Rachel due to her past erratic behavior, she struggles to prove her innocence. Her memories start resurfacing, and she recalls witnessing Tom and Megan together on the night of her disappearance. The shocking revelation dawns upon her—Tom had been deceiving everyone. As Rachel confronts Tom, he turns violent, attempting to silence her permanently. In a desperate act of survival, Rachel and Anna fight back, ultimately killing Tom in self-defense. The truth about Megan’s murder is exposed, and Rachel finally frees herself from the emotional torment of her past, setting the stage for a new beginning.

Paula Hawkins masterfully crafts an intricate thriller that explores the fragility of perception and the devastating consequences of lies. The novel’s multiple viewpoints offer a deep dive into the minds of three women entangled in a haunting mystery, making The Girl on the Train a compelling and unforgettable read.