i think you have to find a dead body or a person who dies... some npc has a note looking for plunkett from the regulators. i think he is at the southern end of the cemetary on the stairway coming out of the metro. at least thats where i found him. it may be different on your game, idk. anywoo, after you get that note he should magically appear in the arlington house --- I do EVERYTHING they tell me not to do on T.V.