Aided by his pet dog, Max, he disguises himself as Santa Claus and breaks into the Whos' homes to steal everything they own and dump it off a nearby mountain. Although he pulls off the theft successfully, on Christmas morning, he is shocked to hear the Whos still singing cheerfully, happy simply to have each other. He then realizes that the holiday has a deeper meaning that he never considered. Inspired, he stops the Whos' belongings from falling off the edge of the mountain, and in the process his heart grows three sizes. He returns all the gifts he stole and gladly takes part in the Whos' Christmas celebration.