Season 1 opens with the LAPD's new Priority Murder Squad (PMS), soon renamed the Priority Homicide Division (PHD), under the direction of Deputy Chief Brenda Leigh Johnson investigates the murder of a technological genius. Brenda has recently joined LAPD after a long career in law enforcement, including with the Atlanta and Washington, D.C., Police Departments. We soon learn Brenda is originally from Atlanta, Georgia, was CIA-trained, and was recruited by her former married lover, Assistant Chief Will Pope. Brenda is resented as an outsider by much of the LAPD and seen as an adversary by Robbery-Homicide's Captain Taylor, who initially persuades her squad to request transfers en masse in an unsuccessful effort to force Brenda's resignation. Brenda soon wins over her assistant, Sgt. David Gabriel, and the grudging admiration of the team when she shows them why she is called a closer; but her battle is far from over. As the season progresses, we see Brenda struggle to establish her authority and earn the respect of her squad, despite the efforts of Taylor and Detective Lt. Andy Flynn to both undermine her authority and hamper her investigations. Slowly, one-by-one, Brenda wins over her team; and, by season's end, she has earned the loyalty of them all, even the hard-boiled Det. Flynn, as they stand united against Capt. Taylor's final attempt to remove Brenda from the squad.

Brenda is now firmly established as leader of Priority Homicide, with her team firmly behind her. The theme for Season 2 is partnerships, which is established as the opening episode centers around an exploration of partnership within the LAPD and in Brenda's life. The theme plays out as the Flynn/Provenza partnership comes front and center early in the season and as Brenda's relationship with Gabriel grows and strengthens while she forms an uneasy working alliance with Commander Taylor. At the same time, Brenda's romance with Fritz grows serious as they make the decision whether they should live together.

The theme for Season Three is family. The PHD has now come together as a unified division, and their stories center on how they function as a family that must cope with a budget crisis. Episodes this season explore issues of family, beginning with a tale of bigamy, and ending with two stories of family pitted against one another. The season also explores the elements of family life in America, the secrets a family keeps and the horrors a family must face. In Brenda's personal life, we meet her father for the first time along with Fritz, with some interesting results. Brenda faces a personal health crisis even as her relationship with Fritz takes a large step forward.