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 train pulls into a station and Ellen is stunned to see the mother hurrying away down the platform, without looking back. Ellen is about to raise the alarm when she discovers a note in the baby's bag with three desperate lines scrawled hastily on it: Please protect Mia; don't trust the police; don't trust anyone...