Alastair Sim was always an excellent comedy actor - his timing and facial expressions always managed to raise a smile for me. Here is has the dual role of the headmistress "Millicent" and of her scheming bookmaker brother "Clarence" as both, in their own way, try to make a killing on an horse owned by the wealthy father of her newest pupil "Princess Fatima". The local village - and constabulary - live in terror of her establishment and of it's rowdy and lawless student body, so they decide to send the plucky and enthusiastic "Sgt. Gates" (Joyce Grenfell) in to masquerade as the games mistress and to gather intelligence as to the dodgy goings on at "St. Trinian's" enabling the law to shut it all down... A solid supporting cast of British actors - George Cole and Hermione Baddeley amongst them prop up well the central dynamic from Sim and the also rather effective Grenfell - another who had super comedy timing. The story is a little cringe-making at times, but the fact that all of the naughtiness comes from these devious and extremely innovative girls makes for a fun ninety minutes of escapades and japes. Plenty of flour fights and who's ever seen an instrument of torture adapted from a laundry wringer? Like so many of the British comedies of the 1950s, it's not comedy that could, or even ought, to be made now - but taken in the spirit of a search for some post war mischief and glee, it's still good fun to watch even now.