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.
While trying out the spy glasses, spy hat, and other items in their new spy kit, seven-year-old Henry and his dog Mudge make a new friend and form a spy club.
When Henry and his dog Mudge go with Henry's parents to visit Great-Grandpa Bill in the home with lots of other grandpas, they lead them all on a wonderful adventure.
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.
While Henry's parents are at a Sweetheart Dance on Valentine's Day, he and his dog Mudge have a wonderful time staying at Mrs. Hopper's house, where they enjoy tea and music and dressing up in various costumes.
After noticing that a visiting hummingbird likes her pink petunias, Annie and her rabbit Snowball, accompanied by Henry and his dog Mudge, fill the garden with pink objects to attract more hummingbirds.
For Henry and his big dog Mudge, spring means admiring the first snow glory, playing in puddles in the rain, and watching the five new kittens next door.