Six Four Season 2 is yet to be announced by ITVX

Michelle returns to Scotland and accompanies Chris in search of Annabel. Robert and Mackie face off as the truth behind Julie Mackie's disappearance threatens to come out.

An unexpected visitor confronts Chris with the consequences of Michelle's secrets. A visit to Gary McLean's killer brings Chris closer to the truth and Annabel faces her captor.

Pauline Wallace receives a ransom call. Chris discovers a link between Annabel's kidnapping and the supposed cover-up in the Julie Mackie case and Michelle confronts Piers.

DC Chris O'Neill is approached by a journalist about a cold case involving a missing girl. His own daughter is also missing, and his wife Michelle goes to London to search for her.