Julieta travels to Guanajuato, Mexico, where she is drawn into a new, head-scratching mystery involving a secret society, mischievous cousins, and the ever-inspiring art of Diego Rivera.

Ten-year-old (and budding detective) Julieta and her family head to Guanajuato, a colonial town in Central Mexico, where Julieta's mother has been hired to restore several paintings from the famous Mexican painter Diego Rivera. Unfortunately, the paintings, which call the breath-taking Diego Rivera Museum home, have been damaged by a mysterious flood. Is it possible that someone damaged the paintings on purpose? Julieta can't help but to want to find out.

Julieta once again finds herself mixed up in an enchanting art-related mystery. Risking a whole lot of parental disapproval and bad grades, Julieta begins investigating a potential Rosicrucian conspiracy unfolding in Guanajuato. But what if the conspiracy isn't real? Is Julieta really wiling to risk disappointing her parents (and eternal grounding) for thieves that may not even exist?

With the help of her cousins Mario, Elissa, and Sofía (lovingly named the MES) Julieta must crack the case to save the work of Diego Rivera, and test the limits of her parents' patience.