To the parents of the warring siblings who attend Camp Happy Harmony, the camp seems a godsend. But after they've been there a while, the campers themselves think otherwise. To them, the six middle-aged Harmony siblings who run the camp seem a little "inharmonious." Soon the campers are deep into finding out just what the dastardly Harmonys have in store for them.
Camp Happy Harmony is where fighting siblings go. Their letters home suggest that something fishy is going on.