A city of Whos on a speck of dust are threatened with destruction until the smallest Who of all helps convince Horton's friends that Whos really exist.

One day, Horton the elephant hears a cry for help coming from a speck of dust. Even though he can't see anyone on the speck, he decides to help it. Good thing since as it turns out, the speck of dust is home to the Whos, who live in their city of Whoville. Horton agrees to help protect the Whos and their home. Unfortunately for Horton, this gives him nothing but torment from his neighbors. They refuse to believe that anything could survive on the...