Betrayal
Throughout the story, characters betray and lie to their loved ones. Tom is the most obvious example. He had an affair with Megan without telling Anna, and an affair with Anna without telling Rachel. He also lies about smaller things such as the army and his parents, betraying trust in his relationships as a whole. Tom betrays Megan herself when he dumps her upon finding out that she is pregnant.
Another example of betrayal is Megan, who betrayed her husband, Scott, by having an affair with Tom and trying to have an affair with Dr. Kamal Abdic.
Craig, Megan's boyfriend, isn't mentioned much in the story, but he was also a betrayer. He left Megan alone after she gave birth to Libby, betraying her trust in a way that permanently damaged her ability to feel safe and trusting in a relationship.
Gender and the Role of Women
Women are central to this novel, beginning with the fact that it is narrated by three women. However, these women value themselves primarily through their looks and ability to have children. Anna is the most secure in herself as she is beautiful, married, and has a child. Megan is somewhat unstable; she had a child in a relationship that fell apart as a result of her inability to care for her child, but she is still confident in her looks and has a husband. Rachel is the most unstable character in the book, and she herself realizes that her downward spiral into alcoholism that eventually caused her to lose her husband and looks resulted from her inability to have a child.
Abandonment
Abandonment is central to the neuroses of Rachel and Megan. Rachel cannot let go of her past relationship with Tom, while Megan acts incredibly hot and cold in her relationship with Scott because she is not satisfied but fears being left alone. This is likely a result of Mac, her boyfriend when she was younger, abandoning her after the death of their child. Megan's fear of abandonment also fuels her troubled relationships with Tom and Kamal in which she is happy when she has power over them but reacts rashly when they attempt to leave her.
Memory
Memory serves as a major source of conflict in the story: Rachel struggles to remember what happened on the night of Megan's disappearance. Her alcohol problem leads to blackouts preventing her from identifying who murdered Megan and realizing the lies Tom told throughout their marriage. In contrast, the inability to forget memories from earlier relationships plagues both Rachel and Megan.
The Self
In The Girl on the Train, many characters must come to terms with their real self. Rachel primarily examines this question through her difficulties reconciling the differences between her sober and drunk self, complicated by Tom's lies about the things she has done while blacked out.
Megan, in comparison, looks at her self across time: "runaway, lover, wife, waitress, gallery manager, nanny, and a few more in between. So who do I want to be tomorrow?" (20). This conflict stems largely from the traumas of her youth - her brother and child dying - which shook her sense of self greatly.
Alcohol
Alcohol is portrayed as a major evil in The Girl on the Train, mainly through its abilities to hinder decision-making and memory. For example, Rachel struggles with alcohol, which results in the ending of her marriage and continuing problems with Tom. Furthermore, her relationships with Scott and the red-haired man are complicated when she drinks with them. However, alcohol is used in the story not only as a catalyst for bad decisions, but also as an indicator that bad decisions are being made consciously, such as when Anna pours herself a glass of wine before snooping on Tom's computer.
Digital Communication
As the book is set in 2012 and 2013, characters appropriately communicate by digital means such as email and text messaging. However, digital communication is important as a theme since it affects the ways in which people can communicate. For example, the paper trail left behind by digital communication leads to Rachel discovering Tom's affair with Anna and Anna getting wind of his relationship with Megan and involvement in her death. The communal sharing of information on the internet and on social media allows Rachel to find Tom's happy posts on Facebook and to contact Scott by looking up his personal website. Furthermore, the ease of digital communication enables Rachel to make poor decisions when drunk and then realize these mistakes the next morning.
