Earnest young tax inspector Cedric Charlton visits the sizeable Larkin family at Home Farm in the countryside. They have not paid tax in an age and he has come to help them fill in their tax forms. However, they get him drunk and, intoxicated as he already is with the charms of the Larkins' eldest daughter Mariette, he decides to stay with them and share their rural idyll.

Pop decides to buy the west wing of the country seat of impoverished aristocrats, the Bluff-Gores, initially for scrap, but Lady Bluff-Gore persuades him to go into the property business. Having rebuffed the advances of urbanite Corinne Perigo, Pop is set up when Mrs. Perigo engineers a situation in which he catches hold of nervous Mrs. Jerebohm to stop her from falling over on a boat. Mrs Perigo encourages the other woman to bring a charge of sexual harassment against Pop.

Pop duly appears in court charged with sexual harassment but Mrs. Perigo is discredited when Pop's brother Uncle Perce, a hotel porter in London, testifies that she is well-known in the big city as rather more of a scarlet woman than she paints herself and the case is thrown out. The day of Mariette's wedding to Charley arrives and, as Charley has no family, the Larkins' friend, the Brigadier, acts as best man after he has got rather cosy with another family friend, the sweet but flirtatious Angela Snow.

The whole family go on holiday to France, a holiday which gets off to a bad start. However, when the family car is seen to have a crest on it, it is assumed that they are titled nobility. Mademoiselle Dupont, the pension's owner, calls Pop 'Milord' and gives him and Ma her bedroom. Even the grumpy receptionist is respectful. Primrose, the second eldest daughter, falls for local boy Marc-Antoine but Charley is annoyed to see his wife cavorting with skimpily clad French hunks on the beach.

A jealous Charley gets drunk when Mariette refuses to go on the local miniature railway, preferring to stay on the beach with the admiring local boys. Pop sobers him up and effects a reconciliation. Mariette finally agrees to go on the railway and enjoys it. Angela Snow and her sister Iris, who are also on holiday in the area, organize a first wedding anniversary party for the Charltons.

The Larkin family plan the quintessential English Christmas, with food, drink and presents galore.