Rachel Watson rides the same train every day, passing by a row of houses where she becomes fixated on a seemingly perfect couple. When she suddenly witnesses something disturbing, she becomes entangled in a missing-person investigation. Struggling with alcoholism and memory gaps, Rachel is unsure of what she truly saw and whether she can trust her own recollections. As the story unfolds through multiple perspectives, hidden truths and dark secrets are revealed, exposing the fragile nature of perception, memory, and relationships.