Coming-of-age story for two girls, Mary Clancy (Hayley Mills) and Rachel Devery (June Harding), who find themselves as students at the St. Francis Academy, a Catholic boarding school for girls. The story spans three years and follows the girls and their many pranks including setting off fire alarms, smoking cigars in the basement, and putting bubble baths in the nuns' sugar bowls. As the girls mature, they gain a greater respect for their teachers and the commitment and devotion required to be a nun, leading one of them to make a life-changing decision.