Oh the thinks you can think when Dr Suess best loved characters collide and cavort in an unforgettable musical caper.

Horton the Elephant is splashing around in the water in the Jungle of Nool one day when he hears someone call, Help! He finds a dust speck and imagines that there are people on it.  He places it safely on a clover. The other animals, especially the Sour Kangaroo and the Wickersham Brothers (monkeys) think hes crazy.  There are people on the speck the residents of Whoville. Horton talks with Mr. Mayor and his son Jojo.  The Cat in the Hat is the narrator, but also enters the story.  He gets Jojo to think which gets him into trouble.

Meanwhile, Gertrude McFuzz, a bird, is sad about her one-feathered tail and Mayzie, a bird with a beautiful tail encourages Gertrude to take some special pills to get her tail to grow, which she does.  Mayzie asks Horton to sit on her egg while she flies off for a vacation, and the monkeys with Vlad the Eagle get the clover with the Whos on it and throw it into a clover field.  Horton is now stuck sitting on the egg when hunters come and sell him to a traveling circus.

Later Gertrude realizes that she wants to go back to being herself and finds Hortons clover for him.  He is brought to trial in the Jungle of Nool and determined to be insane. But he gets the Whos to yell loud enough, especially with Jojos Yopp and they are finally heard. The egg hatches and Horton, with Gertrude, decides to raise the Elephant Bird together.  Its a happy ending!