The programme follows the work of a special police team that investigates "cold cases", which usually concern murders that took place a number of years ago, and were never solved. The team, composed of head officer Detective Superintendent Peter Boyd (Trevor Eve), psychological profiler Dr Grace Foley (Sue Johnston), Detective Inspector Spencer Jordan (Wil Johnson), as well as a number of other supporting characters, uses evidence which has recently come to light, as well as contemporary technology to examine former evidence.