David Robey, a wealthy city merchant and serial killer, blackmails and kidnaps young Callum Aldrich. Chief Inspector John Luther is assigned to investigate the case and promises Callum’s mother, Corrine, that he will find her son. Worried about Luther’s involvement, Robey finds compromising information about the various illegal acts Luther has committed as a police officer, leading to his firing, followed by trial and imprisonment.

Years later, Robey lures Corrine and the parents of other victims where he burns their children’s bodies. She later visits Luther in prison and scolds him for not finding her son’s killer.