Assuming the involvement of the Campbell brothers at the Copeland territory shootout, Jackie confronts Grace, who can no longer sidestep her sons' criminal activity. She is forced to make a terrible compromise. Resenting the outcome of a negotiation that he could not take part in, Decourcy finds comfort in the strength of Siobhan, who keeps her head even after tragedy strikes. Jenny insists on helping Maeve, whether or not that means defying Jackie.
In early 1990s Boston, assistant district attorney Decourcy Ward forms an unlikely alliance with a corrupt yet venerated FBI veteran, Jackie Rhodes. Together, they take on a case that ultimately changes the city's entire criminal justice system.