On the Sunday before Christmas, Dyfed Police were called to a fire at Scoveston Park. As the house blazed, Richard and Helen Thomas, brother and sister, lay dead inside, killed, not by the fire, but by a shot-gun. Police need help to solve a tragic mystery. The parents of Susan Maxwell and Caroline Hogg have waited four and three years respectively to discover who murdered their daughters. Scottish police believe it's not too late for Crimewatch viewers to help.