Rachel Watson's daily commute on the train provides her with a fleeting glimpse into the lives of others, particularly that of a seemingly perfect couple she watches from the train window. The routine takes a jarring turn when Rachel observes something horrific in their backyard, propelling her to alert the police and immersing her in a complex investigation. As unreliable memories from her alcohol-tainted past resurface, she struggles to piece together reality from imagined scenarios. Caught in a web of deception, Rachel must confront her own demons while untangling a mystery that proves appearances can be dangerously deceptive.