Story related achievement; once you meet Bambi "Buck" Hughes (referred to simply as "Buck") after mission 15, there will be five story missions you need to complete before you get to the achievement.
* Mission 16: Piece of the Past
* Mission 17: Down in the Docks
* Mission 18: The Motherlode
* Mission 19: Lin Cong I presume
* Mission 20: Unhappy Reunion
The first of these missions might take roughly 20 to 25 minutes each to complete. Upon completion of the mission, "Unhappy Reunion", you will unlock the achievement.