At twenty-five, Louisa Walker has carefully laid out the pattern of her life: the season in London, a few weeks at fashionable house parties and the rest of the year spent visiting and organizing the lives of her six siblings and their children. Because of her age, refined nature, and strict moral code she is considered to be "Miss Prim." Louisa's guarded existence is disrupted when she accepts an invitation from her sister. She believes that she is simply helping her sister and brother-in-law by watching the children during their travels. However, upon her arrival she meets William, Viscount Woodstone, and an adventure beyond her wildest imagination begins. Starting with the questionable heritage of a baby in her care, she decides to join Woodstone's secret quest to outwit French spies and thwart their evil plan. Despite all Louisa's beliefs, this refined gentlewoman careens around the back roads of England in an ancient cart, poses as a countrywoman, and even saves Woodstone's life. Once the adventure ends, Louisa is concerned that her "Miss Prim" image is shattered, and hopes that Woodstone feels the same emotions for her that she has developed for him.