When new information comes to light about a possible suspect in a year-long unsolved murder investigation, DCI Joanne Davidson appears keen to finally bring Gail Vella's killer to justice. However, after her conduct arouses suspicions, it's not long before AC-12 are on the case. But as AC-12's investigation uncovers deeper and darker information, will DCI Joanne Davidson turn out to be their most dangerous adversary yet?