Paloma is a 12-year-old girl from Kansas who loves mystery novels featuring the fictional detective Lulu Pennywhistle. She is initially reluctant to spend her summer in Mexico away from her friends but quickly becomes fascinated by the culture and the art of Frida Kahlo. She is a careful and logical thinker who cherishes the memory of her late father, keeping a box of notecards detailing stories about his life.

Gael is a 12-year-old boy who plays the trumpet and serves as one of Paloma's Spanish tutors for the summer. He is bold and proactive, recruiting Paloma to help him and his sister solve a mystery regarding a missing ring. He possesses a strong sense of justice and takes immense pride in his Mexican heritage.

Tavo is a seventh-grader who splits his time between Mexico, the United States, and Spain due to his parents' academic work. He is quiet, friendly, and knowledgeable about Frida Kahlo's artwork, often discussing her famous self-portraits. He provides Paloma with her first friendly connection in Coyacán.

Paloma's mother is a dedicated university professor who has earned a prestigious research fellowship in Mexico. She is deeply committed to helping Paloma learn about her late father's Mexican heritage. While loving and encouraging, she is also a protective parent who prioritizes her daughter's safety and education.

Lizzie is a 12-year-old trumpet player and Gael's twin sister. She acts as one of Paloma's Spanish tutors and is initially skeptical of Paloma's courage and ability to help them solve their mystery. She is highly protective of her family and straightforward in her opinions.

Mr. Farill is a university faculty member who helps fund and organize the fellowship awarded to Paloma's mother. He lives in a highly secure, extravagant home and is involved in planning a large birthday celebration for Frida Kahlo at Casa Azul.

Mrs. Farill is Tavo's mother and a university faculty member. She spends her time helping to organize the upcoming party at Casa Azul in honor of Frida Kahlo's birthday.

Mr. Castillo is Gael and Lizzie's father. He works cataloging items at Casa Azul and is deeply loved by his children, who are highly protective of him.

Professor Breton is a faculty member at the local university who is involved with Paloma's mother's fellowship. He also teaches the Mexican Art and Culture class that Paloma attends during the summer.

Frida Kahlo is the legendary Mexican painter whose former home, Casa Azul, serves as a museum. Though a historical figure, her spirit and artwork deeply influence Paloma, appearing in her dreams to offer guidance and serving as a vital link to Paloma's late father.