The Girl on the Train meets the world of social media in this psychological thriller about influencer culture, parasocial relationships, and the secrets we keep from those we love most.

Molly Sullivan is used to sharing intimate details of her life with millions of followers. A thirty-one-year-old single mom, she has built a career out of fearless posts about parenthood and dating. But when Molly shares a photo of her new fiancé, Scott, she is shocked by his negative reaction. For the sake of their relationship, Molly agrees to remove the post and keep Scott and his ten-year-old daughter out of her social media spotlight.

But it's too late, someone has already recognized him. Liv Barrett is certain Scott's the man who killed her sister and disappeared with her infant niece nine years ago. The police don't believe her, so Liv takes matters into her own hands. After driving cross-country to Molly's town, Liv uses her social media posts to orchestrate "accidental" meetings, slowly gaining Molly's trust. Meanwhile, newlywed Molly begins to unpack boxes in her new home and discovers her husband has been lying about his past.

While Molly and Liv uncover secrets that have been buried deep for almost a decade, they have no idea that someone else saw the photo of Scott—someone who poses a threat more dangerous than either of them can imagine. Someone who is watching them from the shadows.