Sim is priceless in a dual role as the eccentric headmistress of a chaotic, bankrupt girls' school and her bookie twin brother who scheme the school into financial security. The first in a series of movies based on a popular British cartoon by Ronald Searles about a girls' school and its mischievous students. Followed by "Blue Murder at St. Trinian's," "The Pure Hell of St. Trinian's," and "The Great St. Trinian's Train Robbery."