Mr. Dingle is the music teacher at Angel Hill Grammar School . He enjoys great respect and popularity among the pupils, not least because of his approachable manner and his appreciation for the jazz played by the school orchestra. This last pastime wins him the disapproval of Mr Frome, the new headmaster, who insists that academic work must come before any extra-curricular activity.
Access to, and funding for, the school orchestra is cut, but after a failed attempt at busking outside the local cinema, Dingle, head boy Nicky and head girl Paulette devise a full-scale al fresco street musical. This proves highly popular with everyone but Mr Frome, especially after he espies a picture of the concert in the local paper. The orchestra is banned, but Dingle undertakes to fund a new set of instruments via an instalment plan arranged by Mr Morris, the father of one of Dingle's pupils.
To earn the money necessary to pay for the orchestra, Dingle takes an evening job playing piano in his local pub, where he is spotted by Routledge, the deputy head. An unheralded visit to Frome's office by a commercial traveller from the instrument supplier alerts the headmaster to the way the new orchestra has been funded, and Frome finally sacks Dingle.
The pupils embark on a campaign of civil disobedience, which escalates from stink bombs in assembly to the wholesale sabotage of a school inspection. None of the punishments that Frome issues seems to have any effect and, in desperation, he summons Nicky in order to arrange a form of truce. This is unsuccessful, and instead inspires Nicky to organise a campaign of utter silence amongst the students. Frome is forced to ask the Ministry to end the term early.
Most of the Angel Hill pupils eagerly take advantage of this extended holiday but the orchestra seals themselves into the music room. Frome visits Dingle at home to tell his erstwhile employee that he will call in the police and then resign as he has clearly failed as a headmaster. Dingle returns with Frome to the school, where he informs the orchestra that he already has a new job and that they have been wasting their time. Frome reveals this to be a lie and ask the children to forgive him for his lack of understanding. Dingle is reinstated and all ends well.
