Not your average girl. Suddenly a princess! Olivia Grace Clarisse Mignonette Harrison sees herself as a completely average 12-year-old schoolgirl. The only things that make her special are her long name and the fact that she is a half-orphan being raised by her uncle and aunt, having never met her father. On a completely average day, when everything goes wrong for Olivia, something incredible happens: a limousine pulls up in front of the school, and Princess Mia Thermopolis of Genovia invites Olivia to come to New York to meet her father and live with them. Because in truth, Olivia is Princess Mia's half-sister and of royal descent. Now she steps into the spotlight and documents her exciting adventures in a diary for her friends.