By chance, a wild boar and a fox are present when a mayfly hatches. They find the happy fly girl quite enchanting, but somehow have to tell her that she only has one day to live. But they can't bring themselves to do that! Instead, they tell the fly that the fox will only live one day. This touches the sensitive fly so much that she wants to give the fox a wonderful last day: he should spend a day that contains all the joys of life.