Arthur and his friends participate in a cooking competition and are worried the judges will be strict food critics. Arthur bakes a chocolate cake for the competition and accidentally uses baking soda instead of baking powder, resulting in an unsatisfying pastry. As a result, he doesn't bring his cake to the competition. However, his father notices and brings in freshly baked brownies and tells Ming Tsai about Arthur's mistake. Ming Tsai then tells Arthur the story of potstickers and how they were an accident to show that even mistakes can bring positive outcomes.
DW keeps a snowball in the freezer from the "best day of her life," but it goes missing. Arthur and his friends and family each recall what happened the day of the snowball's disappearance for each of their own point of view.