As Horton sets out to protect the Whos and their home, he faces numerous challenges from other animals in the jungle who do not believe there are tiny creatures living on a speck of dust. The skeptical animals tease and taunt Horton, urging him to give up his quest and abandon the Whos. However, Horton remains steadfast in his determination to protect the Whos, and even risks his own safety to keep them safe.
Meanwhile, the mayor of Whoville, Ned McDodd, becomes aware of Horton's efforts to protect their city and rallies his fellow Whos to aid in their own defense. Together, they come up with a plan to make their presence known to the larger world, including creating a giant megaphone to amplify their voices and a flag to signal their location.
As tensions rise between the jungle animals and the Whos, the fate of Whoville hangs in the balance. However, with Horton's unwavering support and the Whos' bravery, they are able to overcome the odds and ultimately triumph over their adversaries. In the end, the jungle animals come to realize the error of their ways and embrace Horton and the Whos as their new friends and allies.