<P> Anna is young, beautiful, in love with Tom, and happy as a stay - at - home mother to the young Evie . While at first she enjoyed the idea of showing off to Rachel that Tom picked her over Rachel, she eventually becomes furious at Rachel's harassment of her family . One day, Rachel is stunned to see Megan kissing another man . The next day, after heavy drinking, Rachel awakens to find herself bloody and injured, with no memories of the night before . She learns that Megan is missing, and is questioned by the police after Anna reports having seen her drunkenly staggering around the night of Megan's disappearance . Rachel becomes interested in the case and tells the police she thinks Megan was having an affair . She then contacts Megan's husband, Scott and tells him as well, lying that she and Megan were friends . Rachel learns that the man she saw kissing Megan was Kamal . </P> <P> Rachel contacts Kamal, lying about her identity to get close to him and learn more about him . She makes a therapy appointment with him to see if he can help her recall the events that happened during her blackout that night . While Kamal suspects nothing, Rachel begins to gain insight into her life by speaking with him, inadvertently benefiting from the therapy . Her connections to Scott and Kamal, though built on lies, make her feel more important . She ends up not drinking for several days at a time but always relapses . Meanwhile, she continues to call, visit, and harass Tom . Megan's body is found; she is revealed to have been pregnant, and her unborn child was fathered by neither Scott nor Kamal . As Scott discovers Rachel's lies and lashes out at her, her memories become clearer . Rachel remembers seeing Megan get into Tom's car . Anna discovers that Tom and Megan were having an affair . </P> <P> Rachel begins trusting her own memories more, and realises that many of the crazy things Tom told her she did while drunk never really happened . He had been gaslighting her for years, which made her question her sanity . Armed with this sad realisation, and the knowledge that he must have been the one who killed Megan, Rachel warns Anna . When Anna confronts him, Tom confesses to murdering Megan after she threatened to reveal that he had gotten her pregnant . Anna is cowed, fearing for her daughter's safety . Tom tries to beat and intimidate Rachel into keeping silent but she defies him and fights back . Knowing he is about to kill her, Rachel stabs Tom in the neck with a corkscrew . Anna helps Rachel make sure that he dies from the wound . When the police arrive, former adversaries Rachel and Anna support each other by co-ordinating their stories to explain their actions as self - defence . </P> <P> The Girl on the Train received mostly positive reviews from critics and audiences alike . In 2015 it became the fastest - selling adult hardcover novel in history, and it spent over four months on the New York Times Bestseller List following its release . Kirkus Reviews praised the novel with a starred review, writing that "even the most astute readers will be in for a shock as Hawkins slowly unspools the facts, exposing the harsh realities of love and obsession's inescapable links to violence ." Subsequently, the novel was honoured by Kirkus Reviews as one of the best books of 2015, in the fiction category . The book also won the 2015 Goodreads Choice Award in the category Mystery & Thriller . </P>

Who is the killer on the girl on the train