For Henry and his big dog Mudge, summer means going on a picnic in the park, taking a bath under the garden hose, and going to the top of the big green hill.
At first Henry's very neat cousin doesn't like the cookies from under his bed or Mudge's slobbery kisses, but when they all play frisbee, she begins to enjoy her visit.
Henry and his big dog Mudge celebrate Henry's birthday with a pinata, a lively birthday party, and a cake shaped like a fish tank, making May first the best day ever.