Every morning, Rachel commutes by train into the city, and every morning the train stops at the same spot along the route. Rachel looks into the gardens of the surrounding houses and observes their inhabitants. Often, she sees a young couple: Rachel calls them Jess and Jason. They seem to lead a perfect life—a life that Rachel longs for. One day, she witnesses something shocking. Shortly after, she reads in the newspaper about the disappearance of a woman—next to it is a photo of "Jess." Rachel reports her observation to the police, becoming inextricably entangled in the ensuing events.