Filmed over a period of twelve months, Murder in the Valleys tells the story behind the largest and most exhaustive criminal investigation in Welsh history and its enduring repercussions.

One night in June 1999, three generations of one family were brutally killed in the small village of Clydach, South Wales. For more than twenty years – and despite the conviction of a local builder - the case has deeply divided the community. Now, as the police review the evidence, this series examines a case that didn't end with the guilty verdict.