Does any one remember a post from many years ago that fits this description. The Setting: A man is in his study/living room at night, reading by lamplight. * The Visitor: A man appears suddenly. He is gaunt, weary, and dressed in strange or rugged clothing. He reveals he is a descendant of the man he is visiting. * The Warning: He describes a total collapse of American civilization. He explains that there is a way to stop it, but it requires a specific, seemingly mundane change in the present. * The Cryptic Ending: In the final moments, the visitor...