Blue Murder at St. Trinian’s

With headmistress Amelia Fritton and the teachers out of the picture, St. Trinian's descends into bedlam as students run riot. The Ministry of Education steps in to restore some control, aided by the army. This sets the stakes for the school to regain its status and keep authorities at bay.

Flash Harry launches a marriage bureau, aiming to pair one of the sixth form girls with Prince Bruno. He also leverages a UNESCO offer to fund a Europe tour ending in Rome, hoping it will impress the prince. The plan combines romance with travel as a cover for the school's boost.

Some sixth form girls break into the Ministry and swap the negative inspector feedback file with a positive one designed to cast the school in a better light. The rearranged file is sent back to inspectors, influencing how the school is perceived. This act demonstrates the girls' willingness to bend rules for a chance at the UNESCO tour.

Harry and Myrna learn that a new headmistress, Dame Maud Hackshaw from Australia, is arriving to take charge. They fear she will derail the school's nomination for the UNESCO tour. The impending change heightens the stakes for the students' plan.

On the night Hackshaw is due to arrive, Myrna reveals Joe Mangan's arrival and the police search. They decide to disguise Mangan as Hackshaw and abduct the real Hackshaw, imprisoning her in the school. The plan aims to ensure Hackshaw cannot intervene.

A forged letter from Hackshaw is sent to the Ministry, advising that the girls may partake on the UNESCO tour. With the fake approval, the Ministry seeks volunteers to chaperone and act as interpreters. This step clears the way for the trip and the undercover operations.

Superintendent Kemp-Bird learns of the plan and assigns Sergeant Ruby Gates to go undercover as an interpreter. He also recommends securing coaches from Captain Romney Carlton-Ricketts’s company, the only outfit willing to transport the girls. The aim is to control the tour logistics and monitor everyone involved.

As the group prepares to depart, Mangan remains disguised as a student and accompanies the girls on the tour. He still holds the stolen jewels and hides them in a water polo ball to avoid detection. A sixth form student witnesses this concealment, setting up future trouble.

The tour's stops in Paris and Vienna erupt with chaos as the students push boundaries. The adults try to maintain order while the girls cause mischief, testing the plan's resilience. Romney begins an uneasy flirtation with Gates during the undercover mission.

In Rome, Gates admits to Romney that her cover is blown and that Mangan is among the students. The revelation raises the stakes for everyone involved as they near their final destination. The tour's success now depends on managing the jewel stash and the con of Hackshaw.

During a water polo match before Prince Bruno, Mangan loses the ball containing the jewels and is forced to steal it back. He escapes with the jewels but is chased by fourth-form students. The pursuit ends with his capture at the Coliseum.

Prince Bruno announces his plan to marry Myrna, much to the annoyance of a rival student. The school receives the reward for Mangan's capture, which Miss Fritton keeps for herself and the school upon their return. This victory cements St. Trinian's reputation and finances.

Back in England, Gates parts ways with Romney to join Kemp-Bird, who has been demoted for embarrassment after the Hackshaw incident. The detective duo's future is tied to the school's ongoing adventures. The film closes with the status quo of St. Trinian's restored, at least for now.