In 1939, 17-year-old Mary found herself in an extraordinary position: it was the outbreak of World War II and her father, Winston Churchill, had been appointed First Lord of the Admiralty; within months he would become prime minister. Mary was uniquely placed to observe this historical moment, and her diaries—most of which have never been published—provide an immediate view of the events of the war, exchanges with her father and what it was like to be a young woman during wartime.