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. Danny seeks to uncover the truth behind the murder of a key witness in one of Erin's cases. 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. Frank and his grandson Joe face a difficult decision as they navigate their new and complicated family ties.

Frank struggles after Joe'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 work to solve a murder.

Frank and his grandson Joe 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.