The drama is adapted from the true crime book The Pembrokeshire Murders, written by Senior Investigating Officer Steve Wilkins and ITV news journalist Jonathan Hill.
Two unsolved double murders from the 1980s cast a shadow over the work of the Dyfed Powys police force. In 2006, newly promoted Detective Superintendent Steve Wilkins decided to reopen both cases.
Employing pioneering forensic methods, Wilkins and his handpicked team found microscopic DNA and fibres that potentially linked the murders to a string of burglaries committed in the 80s and 90s. The perpetrator of those robberies was nearing the end of his prison sentence, but if Steve Wilkins was right, he was also a serial killer.
In episode one, newly returned to Pembrokeshire, Detective Superintendent Steve Wilkins looks into a brutal double murder which was never solved. Known locally as the Coastal Path murders, he is shocked to discover links to two other notorious unsolved crimes.
The prime suspect, a local man named John William Cooper, was imprisoned for a number of burglaries and robberies in 1998. If Steve is right, and Cooper is not just a murderer but a serial killer, the team must find the crucial evidence they need to charge him before he is granted parole.
The Pembrokeshire Murders airs 11th-13th January on ITV.