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, and Frank gets a personal request from a woman, Paula Hill, 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.