When siblings Julian, Dick and Anne cannot go for their usual summer holiday to Polseath, they are invited to spend the summer with their Aunt Fanny and Uncle Quentin at their home Kirrin Cottage, in the coastal village of Kirrin. They also meet their cousin Georgina, a surly, difficult girl, who tries hard to live like a boy and only answers to the name George. Despite an uncomfortable start, the cousins become firm friends and George introduces them to her beloved dog Timothy (Timmy), who secretly lives with the fisher boy, Alf, in the village as George's parents will not allow her to keep Timmy.