The girls of St. Trinians are on the hunt for buried treasure after discovering headmistress Miss Fritton is related to a famous pirate.
After wealthy philanthropist Piers Pomfrey has expressed an unusual interest in a ring found by her niece Annabelle, Miss Fritton explains that she is descended from a pirate who, in 1598, stole treasure from another pirate: Pomfrey's ancestor. The location of the treasure is to be found when the ring and its double are put together. Felonious ex-pupil Kelly and Miss Fritton's former lover Geoffrey are brought in to help the school steal the second ring from the evil Pomfrey's misogynistic secret society, leading to a showdown at the Globe Theater, and an amazing revelation as to the identity of pirate Captain Fritton, as well as that of William Shakespeare.
With the students having saved St. Trinian's School for Young Ladies from bankruptcy and head girl Kelly Jones having moved onto some secret assignment, Miss Camilla Fritton, St. Trinian's headmistress, appoints her niece, Annabelle Fritton, as the school's new head girl, a role for which previously meek Annabelle isn't sure she is yet prepared to inherit. Annabelle's mettle in her new role is tested when fellow student Chelsea informs her and the rest of the students that she has been approached by an unknown man to retrieve a ring from the St. Trinian's long not touched archives for a payment of £20,000. The students learn from Miss Fritton that, if the four hundred twenty year old legend holds true, that ring is only one of two when placed together lead to the location of a gold treasure. That legend also includes an on the sea battle between a Captain Lord Pomfrey and a Captain Archibald Fritton, one of Camilla and Annabelle's ancestors. They will all learn that the identity of the buyer is Sir Piers Pomfrey, one of Lord Captain Pomfrey's descendants who must be after the treasure in large part to spite the Frittons. As such, the girls. with Annabelle leading the way, decide they have to beat Sir Pomfrey to the punch by protecting the ring they have on hand, finding the other half of the ring which requires figuring out the puzzle of the legend, and putting the two together to determine the location of the treasure and a way to retrieve it. Because of Sir Pomfrey's connections, the girls believe their task would be aided if Miss Fritton is willing to call in a favor, from now disgraced former Minster of Education and her former lover wannabe Geoffrey Thwaites. In the process, the girls also learn that Sir Pomfrey and the Pomfrey legacy has a grander overall picture, one that strikes to the very heart of the girls as people, and one that they should try to expose, which once again could prove challenging if only because of Sir Pomfrey's stellar reputation as opposed to theirs as delinquents of society.
- St Trinian's 2: The Legend of Fritton's Gold sees the schoolgirls start a new term amidst the chaos and excitement. A rollercoaster style treasure hunt for the legendary Fritton's Gold ensues as they face their most fearsome establishment rivals yet, but the feisty and ever-resourceful girls of St Trinian's are undeterred in their mission to outwit the villainous Sir Peirs Pomfrey and his sidekicks from the women-hating secret society known as AD1.
It starts when an unknown man phones St Trinian's, and gets Celia to find a ring in the school library. She's caught by the other school girls and then explains that the man proposed to give her £20,000 for the ring. The girls believe they can get more, and the Head Girl Annabelle Fritton asks for £100,000. The deal was cancelled for being too high. They talk with the headmistress, Miss Camilla Fritton, and she begins to tell them of Pirate Fritton, her and Annabelle's ancestor. She says he had a treasure hidden somewhere in the world. The ring is half of the answer. There were two rings made, and once fitted together they are the map to the treasure.
That night, the unknown caller turns out to be Sir Piers Pomfrey, the descendent of Lord Pomfrey, a man robbed by Pirate Archibald Fritton in 1589. Sir Piers steals the ring from Ms Fritton, and escapes. The girls then search for the second ring. They begin at the library, where one finds a card with riddles on how to get to the second ring. A 19th Century relative of Camilla and Annabelle's - a Reverend Fortnum Fritton - had found the first ring, and knew how to find the second, but made up more clues for others to find it. It is revealed that they need to dig into Fortnum Fritton's own grave, to get another card. Only half the clue is there, the rest rotted away. Annabelle is suddenly possessed by Fortnum Fritton's soul, and is brought back to the school, where the girls ask the 'spirit' for the rest of the riddle. With the complete riddle, the girls work out the clue, and head off to an all-boys school nearby (based on English boarding school, Eton) to find the next clue, whilst undercover as boys themselves. They enter the headmaster's room, where a hung painting hides the other ring.
With the second ring in their possession, the St Trinian's girls set off to get the first ring, still in the hands of Sir Piers. They begin by doing research about the seemingly wonderful, faultless Sir Piers, and discover he knows Geoffrey Thwaites (played by Colin Firth). Camilla Fritton tracks down Geoffrey Thwaites, whose career had been ruined (by the events at the end of the previous film), and has become a drunk, and clearly heartborken over Ms Fritton and the loss of his career. He tells her Sir Piers is involved in a secret society called AD1. Thwaites then joins forces with the girls, who first help him get over his drunkenness. When Thwaites is back to his old self, he reveals to Ms Camilla Fritton what AD1 actually is - a woman-hating society, existing only to keep women powerless in the world. Annabelle, Thwaites, the young twins, and also ex St Trinian's student Kelly Jones (head girl from the first film) go under cover to AD1 to retrieve the first ring. The attempt fails, and the girls head back to the school. Meanwhile, Thwaites is undercover at the AD1 meeting (which is held at the notable English day school, City of London), when he is called upon by Sir Piers to give his ideas. Thwaites then rants about women and how bad they are, while wearing a camera and microphone that shows the girls at St Trinian's what he is doing. The speech is a ruse to gain Sir Piers trust, and Thwaites swaps the real ring with a fake one, later presenting it to Ms Camilla Fritton.
The rings lead the girls to the Globe Theatre in London. They first create a distraction, knowing they will be followed by AD1 minions - by doing an innocent enough Flash Mob dance at Liverpool St Station. Once escaped they get to the Globe, where they are faced with the actor and actress playing Romeo and Juliet. Romeo duels Thwaites a sword fight and Romeo gets knocked out. Then Ms Fritton knocks out Juliet. Ms Fritton and Thwaites then take up the roles of Romeo and Juliet in an attempt to distract the audience. The girls begin to get close to the treasure while Sir Piers discovers the fake ring and gets to the Globe immediately. They stand in the audience, and because they are a secret organization, must wait until the play is over. But Ms Fritton and Thwaites notice them and begin to stall as long as possible. The girls make it to a secret room and find the treasure. The treasure is Shakespeare's final play: Queen Lear. They find too that Pirate Fritton had 'retired' and decided to become a playwright, and that Shakespeare was Pirate Fritton, but not only that, it was also discovered that Shakespeare/Pirate Fritton was actually a woman. At that moment, Sir Piers enters, takes the Queen Lear script, and says he will destroy it. He always knew about Pirate Fritton being a woman and thought that it should never be known. The girls soon get the payback when they go after Sir Piers, by attacking him pirate-style (complete with cannons) on the Thames, sailing on the Galleon Golden Hind which is located on the south bank to the east of the Globe Theatre.