Well done, the naughtiest girl!1999

When Elizabeth Allen and her friends are back at school. The leaver's concert is planned and there is a tough competition between Arabella Buckley and Elizabeth to play the single piano. When Elizabeth lags behind on the lessons she starts taking it seriously and has a secret hiding place where she reads and learns lessons. When the English paper is stolen and Elizabeth is found red handed and is accused. That night Elizabeth goes missing ......... What happens ?? Who is the thief??