Rachel takes the same commuter train every morning and night. Every day she rattles down the track, flashes past a stretch of cozy suburban homes, and stops at the signal that allows her to daily watch the same couple breakfasting on their deck. She even starts to feel like she knows them. Jess and Jason, she calls them. Their life as she sees it is perfect. Not unlike the life she recently lost.

And then she sees something shocking. It's only a minute until the train moves on, but it's enough. Now everything has changed. Unable to keep it to herself, Rachel goes to the police. But is she really as unreliable as they say? Soon she is deeply entangled not only in the investigation but in the lives of everyone involved. Has she done more harm than good?