The book explores the story of Mia Thermopolis, a ninth-grade pupil living in Greenwich Village with her mother. The events revolving around Mia’s life are written in personal diaries. Mia’s mother and father are separated. Mia spends most of the time with her mother who is a painter. She enrolls in a private school called Albert Einstein high school based in Manhattan. At the school, she meets and befriends Lilly Moscovits. Lilly is a little witty girl with her own TV show that exposes both social and political challenges. While growing up, Mia believes that her father is a European politician.
The life of Mia changes completely when her father visits and informs her that he is the prince of a country called Genovia. Additionally, Mia is the sole child and must take the role of princess. The news catches her by surprise and decides to hide the new developments from everybody. At first, she is doubtful and claims that she cannot be a princess due to her long hair and flat chest. However, it doesn’t take long before journalists visit her school and start interviewing her. Mia is not impressed at first but she has to get used to the new changes in her life.
Popularity is costly. The new role of the princess compels Mia to have a little time for Lilly. The situation puts the two girls in a collision and they stop talking to each other. Later, the two square it out and resolve their differences. Generally, the story explores the themes of love, leadership, friendship, and heartbreaks.