There’s a tradition in a certain section of England that the unwed eldest daughter in a family must wear green stockings when a younger sister gets married. Celia Faraday is forced to do that once, but when her younger sister Phyllis announces she will marry Robert Tarver, Celia refuses to go through that humiliation again and invents a fiance for herself, “Colonel Smith”. To make it seem more real, she writes letters to her “fiance”, but never mails them. One day one of the letters accidentally gets mailed, and is received by a real Colonel Smith, who decides to check out who his “fiance” really is.