On the day that Armistice of 22 June 1940, Prudence "Pru" Cathaway (Joan Fontaine) a strong-willed young woman from the upper class, joins the Women's Auxiliary Air Force (WAAF), a military organisation linked to the Royal Air Force, to her family's surprise. Her aunt Iris and uncle Wilbur disapprove since she has chosen to serve as a private rather than as an officer. However, family butler Parsons privately expresses his support.