Chief Inspector Boyd & his team are back to reopen the files of more cold cases. A spectral leader calling himself The Shepherd is inciting vulnerable women to commit murder; a sadomasochistic killer is counting off his victims leaving the word sorry carved into their skin; & the discovery of an unexploded bomb threatens to bring unforeseen upheaval to the team. Meanwhile Boyds visiting a shrink to deal with his anger management while an apparently mild-mannered ex-con starts to reveal signs that hes actually well connected in a sinister crime ring. Whatever happens whatever the result Boyd is determined to get to the bottom of every crime even if he must examine his own ways of working to unravel the truth. But the final case of the series brings a shocking turn of events that shakes the team to its core.