Twinkle goes to visit her friend Chubbins, who now lives with his schoolteacher mother in the Ozark Mountains of Arkansas. The children take a picnic lunch and walk to a local prominence called Sugar-Loaf Mountain. There, a large stone slides aside to reveal an iron door and a golden key. Entering, the children walk down a long dark passage toward a light at the end: they find that the hollow mountain is occupied by a shining white city made entirely of sugar. The inhabitants are sugar as well. The children are taken to the local king, who welcomes them and gives them a tour of his domain.
Twinkle and Chubbins observe that the society of the sugar people is divided along class lines. The high-class people are made of the purest white spun sugar; those below them are made of brown sugar, while the menial workers at the bottom of the social pyramid are composed of dark maple sugar. They meet two of the king's courtiers who suffer severe social anxieties as a result of this system. Princess Sakareen is so light that she fears she might be hollow inside; Lord Cloy is frosted, and has no idea what his internal constitution may be.
When the party is out riding in the king's chariot, a traffic accident resolves these questions. Sadly, the injured Lord Cloy discovers that he is made of marshmallow within. Princess Sakareen gets better news: her broken leg shows that she is solid through and through, after all. (Her wound can easily be mended, with sugar syrup as a sort of glue.)
There is no water in the kingdom, since water would dissolve sugar; after eating candies and treats, the children are so thirsty that they are glad to leave the sugar land for the daylight world above. Once outside again, they find that they have left the golden key behind, and can never return.
Like the Emerald City, the subterranean sugar town seems to reflect the influence of the "White City" of the 1893 World's Columbian Expedition. Baum describes Sugar-Loaf City as being built of beautifully-ornamented domes and spires and turrets, all in gleaming white.