Two women meet on a train. Each is running from a deadly secret. When one disappears, the other decides to take her place—for better, or for worse.

Jae-young has just left everything she’s ever known, not that it was much. Her thankless job, her infested apartment, her abusive boyfriend—who happens to be dead on the kitchen floor. Murder was never the way she envisioned leaving, but it was desperate times. Now, escaping her transgressions on a train to the bustling city of Seoul, Jae-young is just hoping to become invisible—safe.

On the train she meets a chatty mother with her infant son who seem to be running from a similarly harsh life with her unfaithful husband, hoping to find refuge with the in-laws she’s never met. To avoid further conversation, Jae-young excuses herself for a moment. When she returns, the woman is nowhere to be found, but her crying child remains with a note, pleading with Jae-young to take him to his grandparents in a remote province far from Seoul.

It’s not an ideal pitstop, but for the sake of the child she can’t ignore the request. When Jae-young arrives, the house takes her by surprise. It's a gated manor oozing with opulence and the finest luxuries. Having never met their grandchild or daughter-in-law before, the family assumes Jae-young is the boy’s mother and ushers her in. Then Jae-young realizes: There’s nothing more invisible than becoming someone else.

But both women have ghosts in their pasts. Jae-young may have no idea what lies rotten under the shiny veneer of her new life, but there's nothing she won't do to make sure she never goes back.