The book centers on a genial elephant named Horton, who is convinced by Mayzie, an irresponsible and lazy bird, to sit on her egg while she takes a short "break", which turns into her permanent relocation to Palm Beach. As Horton sits in the nest on top of a tree, he is exposed to the elements, laughed at by his jungle friends, captured by hunters, forced to endure a terrible sea voyage, and finally placed in a traveling circus. However, despite his hardships and Mayzie's clear intent not to return, Horton refuses to leave the nest because he insists on keeping his word, often repeating, "I meant what I said, and I said what I meant. An elephant's faithful, one hundred per cent!" The traveling circus ends up visiting near Mayzie's new Palm Beach residence. She visits the circus just as the egg is due to hatch (after 51 weeks in Palm Beach) and demands that Horton should return it, without offering him a reward. However, when the egg hatches, the creature that emerges is an "elephant-bird", a cross between Horton and Mayzie, and Horton and the baby are returned happily to the jungle, while Mayzie is punished for her laziness by ending up with absolutely nothing.