Mary (Hayley Mills) and her friend, Rachel (June Harding), are new students at St. Francis Academy, a boarding school run by the iron fist of Mother Superior (Rosalind Russell). The immature teens grow bored and begin playing pranks on both the unsuspecting nuns and their unpleasant classmates, becoming a constant thorn in Mother Superior's side. However, as the years pass, Mary and Rachel slowly mature and begin to see the nuns in a different light.