Reeling from a recent divorce and searching to preoccupy her days, Rachel Watson (Blunt) spends her weekday commute to and from Manhattan quietly gazing out the train windows. Every morning and evening, she relives memories from just outside the home once shared with her now ex-husband Tom (Justin Theroux), who now lives there with his new wife, Anna (Rebecca Ferguson), and their baby.
To distract herself from a life that’s grown so aimless, Rachel develops an obsession with the occupants of another house on the route, 15 Beckett Road—a few doors down from where she used to reside. There, blissfully unaware that a stranger is longingly watching, the seemingly perfect couple Megan (Haley Bennett) and Scott (Luke Evans) go about the business of suburban life.
One day, on her way into the city, Rachel witnesses something so shocking in Megan and Scott’s backyard that it rocks her to the core. Soon after, when Megan goes missing and is feared dead, Rachel tells the police what she believes she has seen. But can Rachel trust what she thinks she witnessed, or is she entangled in the crime itself? When one voyeur crosses the dangerous line between concerned and obsessed, she will either find the real killer…or discover that there is innocent blood on her own hands.