Ronald Searle takes us back to the world of the Gothic Public School in ''The Terror of St Trinian's''. In this gloriously anarchic academy for young ladies we witness shootings, knifings, torture and witchcraft, as well as many maidenly arts. The subject of many evergreen films, St Trinian's is synonymous with the sort of outrageous behaviour that would make a convict blench. This book also contains a selection of Ronald Searle's work from the non-school books, including ''The Rake's Progress'', ''Souls in Torment'' and ''Merry England'', etc. and their publication in one volumes stakes Searle's claim to be the greatest and most influential English satirist since the war.