Bumbling but bright-eyed French teacher Laurence Didcott arrives for his first day at The Mansion School, full of enthusiasm and good intentions. The Headmaster's fund-raising efforts to support a new Arts Centre for the school go awry when Laurence makes a disastrous first impression on a wealthy benefactor.

When Laurence gets too wrapped up in the school's Parents Evening, he finds himself trapped into spending the night at the home of the distraught mother of a problem pupil. Meanwhile, he has been assigned to referee a football tournament against a competing school, and he has somewhat too tight a grasp on the spirit of fair play for the staff's liking.

After being nearly trampled by one of Laurence's classes reenacting the French Revolution, the parents of a prospective student bring it to the Headmaster's attention that The Mansion's unruly student body has earned a bad reputation around town. Laurence hasn't set a particularly good example by mowing down an elderly lady with the school minibus on a class outing. When the victim threatens to go to the press, the Headmaster cracks down on the students with a rigorous program of regulations in hopes of salvaging the school's tarnished image. The teachers, finding themselves with empty classrooms and full detention halls, may stage a revolution of their own.

Laurence lands the head of his department, Donald Halifax, in the hospital with food poisoning after cooking him a meal of French cuisine. Eager to prove that The Mansion is a forward-thinking school committed to the European ideal, Headmaster Piper undertakes a search for a dynamic new head of languages in Donald's absence. When debonair, accomplished applicant Dr Chambourcy interviews for the position, it seems Donald is in danger of being put out to pasture; however, left to his own devices, Laurence can be relied upon to smash the Headmaster's dreams of progress, and a few other things in the process.

Temperamental eccentric Gilbert Herring, the school's head of music, has organized the annual student concert in the Swimming Hall for ten years with little support from his colleagues. When Laurence's overzealous attempts to lend a hand bring about abysmal results and drive Herring to hand in his resignation, the concert promises to go far from swimmingly. But with a little further assistance from Laurence, the evening may yet make a big splash.