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.

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 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.

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.

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.

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.

Jackie celebrates a win in front of the cameras but, behind closed doors, he reaches a new low. A shining moment from Decourcy promises a potential future in politics, but any pride Siobhan feels for her husband is squandered by an unexpected betrayal. The Grand Jury reconvenes, and this time Sheik doesn't get off easily. Thanks to Signa's detective work, the Ryan family is now under the watchful eye of the Suffolk DA.

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.

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