The curtain rises to reveal the house of Boy, Sally and Mother. The bird in the tree sneezes, the thunder roars and the rain pours down.

Sally and Boy are stuck inside, as the sun refuses to shine and day turns to wet and cold. Sally and Boy are not happy with being stuck in the house but fear that they must resign to a life of sitting, sitting and more sitting!

As the children fall asleep from boredom, we meet Fish. Fish is swimming and splashing about in his bowl, dreaming of fanciful adventures with whales. Then, a whistle is sounded and something goes "bump." The children and Fish are startled! What could it be?

They come to find that it is the Cat in the Hat. He has arrived to bring fun back into their life. The Cat proclaims that he knows "some new tricks" and begins to play tennis in the house! After he has had enough, the Cat throws the racket away and rides a motorbike. When Cat crashes, though, the Fish warns Sally and Boy that the Cat is mischievous and that he should be gone immediately – Mother is out, and the house is no place for such games.

The Cat assures Fish that he should have no fear and insists that his tricks are not bad. Cat scoops up Fish and begins to juggle him as he stands on a ball... while reading a book... and holding an umbrella... and balancing a cup on his hat!

The Cat is not done with his fancy, new tricks; he has more to show Sally and Boy. Two kittens enter with a glorious cake, another cup and one more book! The Cat juggles all of these items, with Fish in tow. Sally and Boy are astonished by such a feat... but the Cat is not done! The Kittens enter with a toy ship and some milk.

"But that is not all!" exclaims the Cat. The Kittens enter one last time, carrying a third book, a rake and a fan. Miraculously, the Cat balances all of the objects while holding onto the Fish! When Cat tries to proclaim that there is still more to this amazing trick, he falls down and, down with him, tumble all of the things!

There is now a terrible mess. The Fish warns the children that Mother will not be happy when she returns, but Cat refuses to leave. He insists that he will show them another good game that he knows.

A big, red wooden box appears on stage. The Cat says that the game is called "fun in a box," and he begins to open it. Suddenly, Thing 1 and Thing 2 burst out of the box. The children are fascinated with these two, fast-moving creatures. Fish warns them not to shake hands with the Things!

Cat tells the children that Thing 1 and Thing 2 love to fly kites... in the house! The kites bump and bounce off of the walls, their mother's clothing and the furniture as the Things run about the house making a mess. Sally and Boy try to chase after, but they are too fast. Boy is dismayed by such chaos, and the Fish warns that Mother is on her way home.

In a desperate attempt to gain control, Boy grabs a net and chases down Thing 1 and 2. After an exhausting pursuit, he finally snags the creatures! It is now obvious to Cat that the children are not amused by his games. Feeling ashamed, the Cat leaves.

The children are sad for Cat, but the house is now a complete mess. What will they do? Just then, the Cat arrives on a large, cleaning-up machine! Cat scurries to fix the damage and clean his mess. He soon disappears with a tip of the hat.

Mother arrives. She asks the children, "Tell me. What did you do?" Sally and Boy have survived a day with the Cat in the Hat.