The girls of St. Trinian's hatch yet another fiendish plot—a trade union for British schoolgirls. Their friend and mentor, Flash Harry, suggests a plan which involves kidnapping girls from other rather more respectable colleges and substituting their own "agents". Thus begins a hilarious, often bloody, battle of wits as the girls meet resistance not only from Olga Vandermeer, their Headmistress, but from the Minister of Education, a private detective, and an oil sheikh. Despite all his desperate efforts to foil the conspiracy, the Minister has to face a growing realisation that the girls' demands will have to be met—for him this will mean a very great and very personal sacrifice.