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.

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.