DC Chris O'Neill, whose daughter is missing, is approached by a journalist about a cold case involving another missing girl.

Pauline Wallace receives a ransom call, Chris discovers a link between Annabel's kidnapping and the Julie Mackie case, and Michelle confronts Piers.

An unexpected visitor confronts Chris with the consequences of Michelle's secrets, and a visit to Gary McLean's killer brings him closer to the truth.

Michelle returns to Scotland and accompanies Chris in search of Annabel, and Robert and Mackie face off as the truth emerges.