This is that rare beast: a sequel that's better than the first film. Now it's true it gets a fair head-start simply from the fact that it doesn't need to do all the setup that the first film featured, but the film (a) makes the most of that head-start, and (b) steps the farce and shenanigans up to a whole new level. A fact that make clear from the outset, with a rousing rendition of the school song over the opening credits.
Maidens of St Trinian's, gird your armour on.
Grab the nearest weapon; never mind which one.
The battle's to the strongest; might is always right.
Trample on the weakest; glory in their plight!
Blue Murder at St Trinian's opens with 'Flash' Harry spruiking the charms of the sixth form girls to an Italian prince who is looking to marry. It's certainly true that they're an attractive group of young women, and the prince can't pick between their photos. He asks that they come to see him in Rome so he can select a bride. The only catch is that he has to see them well before the school term ends, and the only way the girls could get to Rome would be to win a national scholastic competition, a possibility which seems rather remote.
Of course, the St Trinian's girls are rather more resourceful than people give them credit for. And they're going to need to be, with a diamond thief about to drop into their laps, the police hot on his trail, and them lacking a headmistress to 'supervise' their European excursion ...
This is absurd, slapstick stuff. And it's jolly good fun.