A homeless woman goes missing from a hostel and the team is led to re-examine an old case they all know well. Rick and Greg Knowles, twins who were already suspected in a series of brutal murders of homeless women dating back several years, are back in the frame again. Although Greg is currently in prison awaiting trial for the killings, the team suspect that his brother was actually responsible. Jack leads the charge to make the most of the second chance they have to convict the right man.