In 1928, Rosina Harrison arrived at the illustrious household of the Astor family to take up her new position as personal maid to the infamously temperamental Lady Nancy Astor, who sat in Parliament, entertained royalty, and traveled the world. "She's not a lady as you would understand a lady" was the butler's ominous warning. But what no one expected was that the iron-willed Lady Astor was about to meet her match in the no-nonsense, whip-smart girl from the country.

For 35 years, from the parties thrown for royalty and trips across the globe, to the air raids during WWII, Rose was by...