The hunt to catch the killer of three young women in the Port Talbot area in 1973 and the remarkable story of how - in the first case of its kind - the mystery was solved almost 30 years later using pioneering DNA evidence. Contrasting the policing methods of the 1970s with the forensic breakthroughs of the early 2000s, the series portrays a town dealing with the repercussions of an unsolved case three decades on, and asks if justice can ever truly be found.
The series tells the story of detective DI Cadi John who returns to north Wales to care for her ailing father. However, when the body of a young woman is found in a local river, Cadi's world - and the world around her - is changed forever.