The Girl Who Owned a City/Headscratchers

• Exactly how fast did this plague come through? It took long enough for the parents to train and prepare their children a bit, but not fast enough for adults to set up a counsel of responsible preteens to handle things (or at least try to) when the adults are all gone? If it took a while, what happened to the children who crossed the age threshold in the interim? It took place long enough ago that most infants have grown to a more "manageable" age without needing to be breast fed (or they're gone already), so it couldn't have wiped through that quickly.