Murder mysteries rely on witnesses, and problems arise when the witnesses are unreliable. Rachel isn't unreliable because she's a liar; she's unreliable because she literally can't remember what happened, no matter how hard she tries. Almost every theme in The Girl on the Train branches off from Rachel's alcoholism, and her memory is no different. At times, it feels like Rachel's past lies at the bottom of a bottle. She can't see it through the alcohol, but if she drinks it all, she'll pass out before she sees what lies beneath. The first two-thirds of the book are Rachel's struggle to remember.
Questions About Memory and the Past
What does Rachel remember at the end of the book, and how does her recovered memory change your perception of certain characters?
If Rachel didn't have memory loss, how would the book be different?