Ellen was just trying to help a stranger. That was how it started: giving a few minutes respite to a flustered young mother sitting opposite her on the train. A few minutes holding her baby while the mother makes an urgent call. The weight of the child in her arms making Ellen's heart ache for what she can never have. Five minutes pass. Ten. The train pulls into a station and Ellen is stunned to see the mother hurrying away down the platform, without looking back. Leaving her baby behind. Ellen is about to raise the alarm when she discovers a note in the baby's bag, three desperate lines scrawled hastily on a piece of paper: Please protect Mia; Don't trust the police; Don't trust anyone. Why would a mother abandon her child to a stranger? Ellen is about to discover that the baby in her arms might hold the key to an unspeakable crime. And doing the right thing might just cost her everything.