The story begins with a girl named Rosaura arriving at the house of her friend Luciana, who is having a birthday party. Rosaura goes straight to the kitchen to check whether a monkey is being kept there, and she is relieved to see that it is. Earlier, she had argued with her mother, who told her that it was nonsense to expect to find a monkey at the party. Her mother had been annoyed by the prospect, calling it “a rich people’s party.”

Rosaura’s mother works as a cleaner for Luciana’s parents. Before the day of the party, she tells her daughter that Luciana is not really her friend and that the family regards her as nothing more than the daughter of a servant. This upsets Rosaura, who says her mother knows nothing about friendship. She loves Luciana’s big house and her family. When Rosaura’s mother refuses to believe that the party will feature a magician with a tame monkey, she takes this as an insult to Luciana’s parents, saying that it is unfair for her mother to call them liars just because they are rich. Rosaura desperately wants to go to the birthday party, but does not know whether her mother will allow her to do so. However, on the day of the party, her mother has starched her best dress in preparation, and she washes Rosaura’s hair.

As soon as Rosaura arrives at the party, she asks Luciana about the monkey, and goes to the kitchen to look at it. The monkey seems to be deep in thought, and its comical appearance fascinates Rosaura. From time to time during the course of the party, she slips away and returns to the kitchen to look at it again.

At the party, a blonde girl with a bow in her hair asks Rosaura who she is. Rosaura says that she is a friend of Luciana’s, but the girl retorts that she is Luciana’s cousin and knows all her friends. She interrogates Rosaura about how she knows Luciana, until Rosaura finally admits that she is the daughter of a family “employee.” The girl continues to insist on knowing exactly what her mother’s employment is, until Luciana’s mother, Señora Ines, intervenes and asks if Rosaura could help to serve the hot dogs.

Apart from her encounter with the blonde girl, Rosaura has a wonderful time at the party. She passes out the cake, which makes her feel powerful, as she is able to give Luciana and the boys large slices, and the blonde girl the smallest slice. Then comes the magician, with his monkey assistant. For his last trick, the magician makes the monkey disappear, asking for one of the children to hold it as he does so. He selects a fat boy from the audience, but the boy is frightened and drops the monkey, so Rosaura takes his place. The trick is a triumphant success, and before Rosaura returns to her seat, the magician says to her, “Thank you very much, my little countess.”

When Rosaura’s mother comes to pick her up from the party, Rosaura immediately tells her about helping the magician, noting proudly that he called her a “countess.” Until that point, she had thought she would be angry with her mother and confine herself to pointing out that the monkey was there, just as she had said it would be.

As the children leave, Señora Ines hands out gifts to all the children. To the boys, she gives yo-yos in blue bags, and to the girls, bracelets in pink bags. Rosaura would rather have a yo-yo but says...