DCs Jo Masters and Mickey Webb investigate the death of a teenage girl from a suspected heroin overdose, who Jo recognises as Kelly Porterfield, a girl she previously arrested for soliciting. Jo breaks the news to Kelly's mother Helen, who reveals that Kelly had run away with her boyfriend Andy Donnelly a year earlier. When the prints on the syringe turn out not to be Kelly's, a murder enquiry is launched. Jo and Mickey quiz Andy at his flat and find him living with 14-year-old Jen Kilshaw. Andy says Jen is just a friend and that he and Kelly broke up months ago. But as the case develops, Jo discovers that Andy got Kelly hooked on drugs so he could control her and she fears he's doing the same to Jen. Jo visits Jen again and tries to make her see that Andy is bad news - but Jen says they love each other. When it's confirmed that the prints found on the needle that killed Kelly belong to Jake Clegg, a name that has frequently cropped up, Jo and Mickey realise that Kelly's death is part of a national network of trafficking underage girls - and Andy and Jake are involved. That night, Jo takes Jen back to her residential unit and chases away Andy, who has been waiting outside. Deciding not to take any chances, Jo gets into her car and prepares to sit it out for the night to keep Andy away from another vulnerable young girl...
