My setting is a post-apocalyptic world, where the event that destroyed civilization was a plague that wiped out most of the planet. The ones who survived (about 40 in this particular city) contracted the strain that destroys memory. They've retained language, basic survival instincts (including the human "herd instinct"), and occasionally some if the more deeply ingrained social mores. Not a single one remembers his or her name, or family (though some family ties have been reestablished by inference), or job, or how to operate technology of any kind. There may be one person who can still read.
By the time the story starts, the survivors have already banded into a sort of society led by one man and his presumed wife. The two have proven their fitness for office by now, but for the sake of background how could they first earn the trust of the masses long anough to be listened to?