As Decourcy prepares to take Sinclair Dryden to trial, despite pushback from the Suffolk County DA, Jackie tracks down a key witness. Siobhan reaches a settlement on behalf of the Mendoza family, but her moment in the spotlight is cut short. Caysen is offered a second chance by a loved one. Reckoning with the rifts in her own family, Jenny meets her long-lost half-brother. Season finale.

When an unlikely source confides in Decourcy, the Massachusetts State Police hatch a plan that promises arrests without the help of the FBI. However, keeping out of the way is not exactly Jackie's strong suit. The Genesis Coalition pitches a new strategy to curb Boston's crime rate. Jenny opens up about her past to a sympathetic ear.

As Jenny grows closer to Diarmuid Doyle, her unwitting husband Jackie is released from the hospital — and he's after revenge. Siobhan calls on Decourcy for help cornering Needham Industries as she fights to expose the corporation's malfeasance. After a break in the case against Sinclair Dryden, the DA's office bumps up against an unforeseen obstacle.

Jackie celebrates another moment in the spotlight, though an unfamiliar pang of guilt leaves him reflecting on his legacy. Decourcy considers the best course of action to finally carry out justice for the murdered guards. Jimmy is desperate to weasel his way out of the mess he's created, even if it means putting his brother's future into question. Jenny faces what has been haunting her all these years. Season finale

As Boston mourns another loss, Decourcy pursues justice in and out of the courtroom. Despite his maneuvering, Jackie discovers that he can't escape his past, while Jenny decides to finally confront hers. Cathy says goodbye to the root of her struggles. Siobhan sets her sights on a new dream.

With the gang's arms dealer in custody, Jackie thinks he's a step closer to glory. But Decourcy is the one in a position to negotiate and he's considering cutting off the gun supply rather than going after the buyers. Jimmy and Frankie must find a new dealer as they prepare for their next job. Cathy and Jenny struggle to comfort their daughters who've undergone trauma. When Michaela falls into some trouble, Rachel decides to take her investigation into her own hands.

As U.S. Attorney Karen Shimizu tries to get rid of her troublesome agent once and for all, Jackie schemes his way into a new mission. At the Suffolk County Courthouse, Decourcy and Siobhan spar on opposing sides of a legal battle. Meeting dead-ends at every turn in the effort to help her son, Grace does something desperate. With a nudge from Maeve, Jenny surprises Benny with some rebellious fun. On the other side of town, Cathy re-ups her supply by going straight to the source.

Decourcy is a step closer to connecting the stolen guns to the Revere robbery when an insider agrees to talk. Jenny is no longer able to ignore Jackie's indiscretions after they show up on her doorstep. An unexpected rush to the hospital worsens money problems for the Ryan family and Reverend Fields discovers that his longstanding influence doesn't make him invincible.

In early ‘90s Boston, racism is endemic and crime is widespread. Jackie Rohr, a renowned FBI agent whose methods are not exactly by the book, does not mind the status quo. But Decourcy Ward, the new Assistant District Attorney in town, wants to uproot the corrupt system. The two form an unlikely, and obligatory, alliance to take down a gang of armored truck robbers from Charlestown.

Jackie strong-arms Jimmy to get a step closer to finding the presumably dead armored truck guards. Decourcy rattles a suspect called to testify before the Grand Jury. Siobhan learns something unsettling about a leader of the Coalition and worries it could jeopardize the future of the group. Kick's nightmares continue as she senses her father might be in harm's way.

After an eventful Sunday at church, Decourcy finds out he has a new powerful enemy in town — one that puts his wife Siobhan in an awkward position. Jackie is stirring up trouble in his own home, and his distrustful mother-in-law Rosa is onto him. Investigators Hank Signa and Rachel Behnam look into an unsolved missing persons case connected to the robbery in Revere. That could mean trouble for Frankie Ryan, who's busy laundering his most recent loot and, with the help of his brother Jimmy, getting carried away in the process.

As Decourcy increases pressure on the Justice Department, Jackie counters by looking into his adversary's romantic past. While Jackie's digging up dirt, Siobhan is planning ahead, focused on starting a family even as Decourcy remains preoccupied by the escalating conflict. Jenny realizes she can't keep ignoring her mother after an unsettling phone call. With business at the salon all but dead, Cathy Ryan turns to an unlikely income source.

When an assistant U.S. attorney overdoses and ends up left for dead, Decourcy Ward suspects Jackie Rohr's involvement. Jackie, in turn, goes after the BPD for a questionable drug arrest at Braxton Summit, a federal housing project. Community activist Grace Campbell recruits Siobhan Quays to work on behalf of Braxton and its residents, but their efforts are subverted as tensions flare between rival gangs.

Jackie searches for his absent informant as Jenny searches for purpose, revisiting her passion to become a teacher. Decourcy works up a plan to overcome the town's infamous "Code of Silence" and get a few suspects to talk. Minogue is assigned a big case, but not the one he actually cares about. Jimmy skips town to visit his kids and finds that, even a thousand miles away, he's not safe from his problems back home.

Jackie and Decourcy continue to hunt down the weapon connected to the armored truck robbery in Revere. Michaela Freda, a local reporter, gets a tip about a story that could lead her down a treacherous path. Despite the threat of a Grand Jury, Frankie considers what he must do to provide for his family. Pressure on Siobhan begins to mount. After another allegation is brought to her attention, she questions whether doing what is right is ultimately what is for the best.

As Jackie continues his fling with Letitia Dryden, Jenny sets out to get her husband reinstated in the FBI. The pressure on Decourcy mounts when a colleague competing for the position of DA lands a conviction. Caysen testifies at the federal trial of Tony Suferin and is blindsided by the consequences. A threatening interaction offers Siobhan a sense of what exactly she is up against in her fight for the Mendoza family.