Inspired by British cartoonist Ronald Searle's St Trinian's School comic strips, the film focuses on students and teachers of the fictional school, dealing with attempts to shut it down while the headmistress faces financial troubles, which culminates in students thwarting a scheme involving a racehorse.

The Sultan of Makyad enrols his daughter Fatima at St. Trinian's – a girls' school in England, run by its headmistress Millicent Fritton.

She discovers that Millicent prepares her students to succeed in a merciless world by fighting authoritative figures in the police and government.

[12][13] Kine Weekly said "Wacky, side-spitiing collegiate extravaganza, based on Ronald Searle’s grotesque, though wildly funny, drawings, illustrating odd, unseemly goings-on at a young ladies’ seminary.

Alastair Sim fills the dual role of headmistress and her bookie brother, and his sly sense of humour holds the chapter of lunatic incidents firmly together.

A first-rate supporting cast packed with experienced adults and eager youngsters, and liberal staging put the finishing fouches to another sure winner from The Happiest Days of Your Life stable.

"[14] The New York Times wrote, "Credit Alastair Sim with doing excellently by the dual roles he essays ... Joyce Grenfell makes a properly gangling, awkward and gullible lady sleuth; George Cole does a few delightful turns as the conniving Cockney go-between and last, but not least, the Belles of St. Trinian's rate a vote of confidence for the whacky freedom of expression they exhibit.

In 1954 nothing had ever been seen to compare with this anarchic adaptation of Ronald Searle's cartoons, which turned traditional ideas of female gentility on their heads.

Alastair Sim's Miss Fritton and George Cole's Flash Harry became icons of British comic lore, but the real star of the film is Joyce Grenfell.