The protagonist in this great story is twelve-year-old María Luisa, better known as Malú. Starting at a new school at this age is never easy, and Malú's first day at José Guadalupe Posada Middle School is no exception. It turns out that her punk-rock look violates school code, which leads to her mother, who is both Mexican-American and a teacher, being disappointed in her.

Malú gets to know various characters as she adapts to her new life, including Joe Hidalgo, whose parents own a coffee shop called Calaca Coffee, which is close to Malú's new home. Joe will be one of the members of the band that Malú helps to start, which is called The Co-Co's. Other important characters include Benny and Ellie, who are the other members of the band.

She soon meets Selena Ramirez, who is one of the most popular girls in her class and the antagonist in this story. She tries to sabotage an event that The Co-Co's have worked hard to put together by going to the school principal with her concerns.

The final significant character who we meet is Malú's father, who flies in from Florida to see Malú and the band performing at the Fall Fiesta. Having him there helps Malú to reconcile the two parts of her heritage: the Mexican roots that she has inherited from her mother and the love of punk that she got from her father.