Jed Mercurio's smash-hit crime thriller returns for its sixth instalment, with Martin Compston, Vicky McClure and Adrian Dunbar reprising their roles as DS Steve Arnott, DI Kate Fleming and Superintendent Ted Hastings. New information comes to light about a possible suspect in a year-long unsolved murder, and DCI Joanne Davidson (Kelly Macdonald) appears keen to finally bring Gail Vella's killer to justice. However, her conduct soon arouses suspicion, and it's not long before AC-12 are on the case. But as their investigation uncovers deeper and darker information, will Davidson turn out to be their most dangerous adversary yet?