Quentin and Becca are a couple of survivors you meet during the game that are part of another settlement. Quentin will ask you to look into Becca's past for him in a mission called " A Discreet Request " because he is unsure about the relationship. Once you get the information from the local Sheriff you will want to keep the information to yourself and tell Quentin that the past is best left in the past. The achievement will unlock after you tell him to move on.