It's The Man with the Yellow Hat's birthday and George wants to throw him a surprise party. The Doorman tells him what he needs to throw a good party, which includes cake, decorations, and friends. But George picks the wrong sizes for everything which leads to disaster. Then George has a dream about what the world would be like it if were monkey-size and decides that in a people-sized world, it is simply a matter of measuring to find the right size.