Harlee Santos (Jennifer Lopez) is a charismatic single mother and resourceful detective at the heart of a tight-knit crew of Brooklyn detectives, led by enigmatic Lieutenant Matt Wozniak (Ray Liotta), who often leads the team to step outside the limitations of the law in order to effectively protect their precinct and their own.

Harlee navigates her fractured relationship with Wozniak as she struggles to conceal her deepest secret: She killed her daughter's father. Following his discovery that Harlee collaborated with the FBI, Wozniak is confronted with a gut-wrenching dilemma of his own. The crew is under tight scrutiny from Stahl and the FBI as well as from Internal Affairs, in the form of a gregarious detective, Verco.