[1] 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 in the past, and were never solved.

The team, composed of head officer Detective Superintendent Peter Boyd (Trevor Eve), psychological profiler Grace Foley (Sue Johnston), and 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.

Initially, Boyd, Grace, and Spence were accompanied by junior DC Mel Silver (Claire Goose), and stern forensic scientist Frankie Wharton (Holly Aird), but both left after the end of the fourth series.

Although the plotlines generally centre around the case, other storylines have been incorporated across the years, including Boyd's anger-management issues and his being reunited with his son, Grace suffering from cancer, Spencer being shot at the hands of one of his former colleagues, and Mel's death, which creates a chain of events lasting across two series.

Some of the issues were dealt with through the conflicting views of Peter Boyd (a white middle-class liberal) and Spencer Jordan (a black working-class conservative).

The sixth series began with strong ratings, with "Wren Boys" achieving 9.2M viewers and a 35.2% audience share.