After getting a match from an unknown relative from a DNA network, Sean Reagan does some detective work to figure out who this mystery person might be. Frank gets a personal request from a woman to transfer her son to a safer assignment. Also, Danny seeks to uncover the truth behind the murder of a key witness in one of Erin's cases, and Eddie begins to think about having a child after she and Jamie discover a newborn left outside their precinct.

Danny and Jamie combine forces to convict a notorious drug lord, as Erin nervously awaits the Governor's selection for the new District Attorney. Also, Frank and his grandson, Joe Hill (Will Hochman), face a difficult decision as they navigate their new and complicated family ties.

Frank struggles after Joe Hill's lineage as a Reagan is revealed; Erin and Anthony receive gift-wrapped evidence; Danny's opposition to authority clashes with Jamie's adherence to the rules, as both brothers work to solve a murder.

Shockwaves ripple through the Reagan family when Danny discovers that their newest family member, Joe Hill (Will Hochman), is working undercover for the ATF to bring down a gunrunning organization.

The Reagans band together to prevent Joe Hill from being killed in the line of duty like his father when they fear Joe’s cover has been blown within the gunrunning outfit he’s helping the ATF bring down.

Frank causes family tension when he assigns Jamie to guard Danny after a hit is put on him; Frank tries to stop his grandson from seeking revenge after he’s attacked; Eddie gets a hostile new partner.

Frank is at odds with his friend Archbishop Kearns when he says the NYPD arrested the wrong man for a murder; Eddie tries to get justice for a sexual assault survivor; Jamie and his nephew, Joe Hill, butt heads over fair police practices.

Erin's nephew, police officer Joe Hill, becomes aware of witness tampering in a trial; Baez forces Danny to help her find the killer of her favorite TV personality; Eddie questions her decision to become a police sergeant.

Jamie and Joe search for an undocumented teenage girl who has been sex-trafficked; a woman in witness protection is murdered; Frank calls out the district attorney's office for instituting a new rule that classifies armed robbery as a misdemeanor.

Eddie and Jamie deal with a domestic violence case associated with an investigation lead by Danny and Baez; Frank and his friend go on a mission to avail themselves to an unfiltered look at the city; Erin is presented with a surprising offer.

Danny and Jamie clash over a gang-related shooting; Erin and Anthony search for answers when a lawyer in their office jeopardizes a case involving Erin's nephew; Frank grows concerned when he's not invited to speak at a policing forum.

Frank and his grandson, Joe Hill, contend with a grievous insult to the memory of Joe's father; Erin and Henry work together to bust a scammer targeting the elderly; Eddie's captain takes suspicious interest in her efforts to locate a stolen puppy.

Danny and Baez race against the clock to catch a serial killer targeting young women; Erin and Eddie clash when Eddie intervenes in a murder case and Erin's personal life; Frank must decide how to discipline his grandson.