When she mistakenly receives an offer of work addressed only to "Mary Brown," the lonely young heiress Mary Thornton Brown forms an audacious plan--to spend her summer not as a guest at a fashionable resort but as a hired girl in Mrs. Roberts' boarding house. Over the course of her adventure, she meets people from many different walks of life, a number of them, to her amusement, sharing her own last name. A certain gentleman boarder is particularly pleasant--but even he is not the best friend Mary will meet during her summer at Mt. Hermon.