Twenty-five year old Cardew Robinson is the oldest pupil at St. Fanny's School which, under the terms of the Robinson Will, receives the entire income from the estate so long as Cardew remains at the school.

While incompetent teachers ineptly continue their attempts to educate their insolent pupils, the solicitor to the estate, McTavish, is suspicious of the headmaster, Dr Jankers, and hires a tough private detective to investigate him.

Jankers is in the toils of a shady bookmaker, Harry the Scar. He does his best to get Cardew expelled and thereby disinherited, so that the estate will pass to St. Fanny's.

During a trip to an art gallery, Harry and his co-conspirators Ferdy and Maisie arrange to plant a stolen painting on Cardew. Numerous complications ensue before the St. Fanny's annual concert, by the end of which Cardew's name is cleared, and he finds romance with Maisie.