Initially, Boyd, Grace and Spence were accompanied by junior DC Mel Silver (Claire Goose), and stern forensic scientist Frankie Wharton (Holly Aird), however both left after the end of the fourth series. Felix Gibson (Esther Hall) and Stella Goodman (Félicité du Jeu) replaced them in the fifth series, before Eve Lockhart (Tara Fitzgerald) replaced Felix from the sixth series onwards. Katarina Howard (Stacey Roca) replaced Stella in series eight, while Sarah Cavendish (Eva Birthistle) replaced Katarina in series nine. 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 re-united 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.