Even though her brother Arthur says she is too little to help with the upcoming wedding, D.W. proves she is just the right size when disaster strikes during the ceremony.
Arthur and his friends are getting ready for a new day of school, but when it turns out that Arthur has forgotten his homework, it is his (sometimes) annoying little sister, D.W., who saves the day.
It is Muffy's Spring Fling party, and Arthur is so slow that he comes in last in every game--except for the jelly bean hunt, where not finishing early proves to be an advantage.
Arthur's science project is a model of the human heart, and when excited Pal the dog breaks it Arthur is upset and tells his friends that his heart is broken--and as soon as they understand the problem they band together to set things right.
