The film tells the story of how the Pettigrew family, living in their family estate Kiloran House in Scotland, deal with changes brought by the end of World War I, told through the point of view of one of the Pettigrew children, Fraser. The family is headed by the maternal grandmother MacIntosh, affectionately known as "Gamma", whose decisions are to be obeyed without question. Gamma's son Morris left home to build a career for himself and succeed as a well-to-do businessman; while her younger daughter Moira followed the traditional route - she fell in love with Edward Pettigrew, gave up a promising chance at becoming an opera singer, settled down at her family estate and raised a large family. Edward is a typical country gentry of his time - owns a minor business, a pious man and defender of traditional values, loves and listens only to Beethoven and has a passion for inventions and mechanical improvements all over the estate. All of which are laughed at by Morris, who lives in London but comes back to visit often, as he is competing with Edward to inherit the estate after Gamma passes away; the two can barely conceal their loathing for each other. Edward does not appreciate and resists waves of new changes in the world, but the harder he tries, the more things fall apart. Morris and his beautiful and charming French fiancée Heloise introduce jazz to the children. An emergency landing brings the eldest daughter Elspeth's first suitor - French show pilot Gabriel Chenoux. Fraser discovers grandfather MacIntosh's book collection in the attic, and as an act of rebellion against Edward, sets out to read them all. Without guidance, he misunderstands the definition of "prostitution", and believing it to be a business term, suggests to all guests at Morris and Heloise's engagement party that Moira, Heloise and Gamma should go into prostitution to enhance the moss business. Worst of all, Edward finds himself drawn to Heloise, and makes a pass at her prior to the wedding. While passing out food during a curling game held in her husband's honor, Gamma falls through the ice into the lake. Although she is pulled up immediately, she dies of pneumonia soon after. Gamma's will leaves the estate to Edward, leading to the ultimate altercation between Edward and Morris at her wake. Edward boasts that Morris has lost more than the estate to him, causing Moira to finally confront him and tell him that she has been aware of his affair with Heloise all along. It takes months before Edward's efforts finally win back Moira, and the family settles back into its old routine. On a Sunday morning, all Pettigrews are heading to church, except Fraser. Edward finds him relaxing in a chaise longue in the library, a cognac glass filled with milk in one hand and a lit cigar in the other, swaying his head and body to a gramophone recording of Louis Armstrong's "On the Sunny Side of the Street". Instead of being thrown into a fit of rage, he smiles and closes the door, leaving Fraser to enjoy himself.
