Blue Murder at St. Trinian’s

A jewellery thief who appears at St. Trinian's and becomes entangled with its capers. He disguises himself as Dame Hackshaw to dodge the authorities and to help the girls, showing resourcefulness and a protective streak toward Myrna. His on-and-off pursuit for stolen jewels propels the plot toward a tense climax at the Coliseum.

The new headmistress recruited from Australia, she represents an outsider who unsettles St. Trinian's. Her planned arrival is sabotaged by the students who abduct her, forcing a swap with the impersonator. Her role becomes a catalyst for the UNESCO tour and the ensuing misadventures.

The formidable headmistress of St. Trinian's who embodies the school's wrinkled charm and leadership. She maneuvers through the chaos, ultimately benefiting from the outcome of the jewel capture and the school’s notoriety. Her presence anchors the film’s satirical lens on education and authority.

A crafty business associate who schemes to monetize the girls’ exploits by arranging a marriage bureau tied to the royal prospect of Prince Bruno. He capitalizes on the UNESCO tour to advance his plans, shaping the caper’s logistics and the girls’ involvement.

A real royal in the background plot who is to decide on a marriage with one of the sixth form girls. His looming option provides motivation for Flash Harry’s matchmaking scheme and sets up the final romantic tension of the story.

Daughter of Joe Mangan, she becomes central to the plan and the emotional core of the caper. Her loyalty to family drives key decisions, and she helps reveal her father’s presence to the authorities. She navigates the crossing between affection and crime with surprising resolve.

The undercover police sergeant assigned as an interpreter to oversee the students during the tour. She discovers Mangan among the group and becomes a critical link between law enforcement and the running caper. Her capture of the ruse adds to the film’s investigative tension.

The local police chief who is anxious to arrest Hackshaw and bring order, but is hampered by bureaucratic missteps. His failure to apprehend Hackshaw leads to embarrassment and a formal demotion, a point of comedic critique on authority figures.

A supporting student figure who contributes to the school’s caper dynamics and social circle. Her participation reflects the ensemble nature of St. Trinian's mischief and the charm of the girls’ collective schemes.