Off-duty police officer Laurie Franklin finds herself caught up in a strange sequence of events after a person falls in front of her train.

When she learns that a newborn baby has been abandoned at the local hospital Laurie becomes convinced that the two events must be connected, but both the train's victim and the baby remain unidentified.

As she is drawn deeper into the mystery, Laurie realises this might not be a simple case of suicide at all, but something much darker.

A week on, and with no new leads, Laurie and Mal carry out a reconstruction of the events of that fateful day and this provides some surprising encounters. With baby Michael in danger, speculation is rife about the whereabouts of his parents. Laurie has an unsettling encounter with train driver Pat and starts to realise he might know more about the case than he first let on. Family tensions mount for Nusrat and Danny when they realise that their new visitor is hiding a very dangerous past.