Despite her sheltered upbringing, Jenny is a teen with a bright future; she's smart, pretty, and has aspirations of attending Oxford University. When David, a charming but much older suitor, motors into her life in a shiny automobile, Jenny gets a taste of adult life that she won't soon forget.

When their beloved school is threatened with closure should the powers that be fail to raise the proper funds, the girls scheme to steal a priceless painting and use the profits to pull St. Trinian's out of the red.