Listen to Leanne's story about the Master

 is an unmarked quest in Fallout 2.

Walkthrough
When you first talk to Leanne at Becky's casino in the Den (right across from Rebecca), tell her that your ancestor was the one who killed The Master, she will then ask you to buy her a Nuka-Cola. Afterwards she will tell you the story about The Master and you will receive 350xp.