Mundy provides a history of female crytographers during World War II. At the outset of the war, cryptanalysis, the science of deciphering coded messages, had barely emerged and both allies and foes outpaced the United States. With young men galvanized to serve overseas, women were actively recruited on the home front. Initially, this effort focused on students from the Seven Sisters colleges but eventually expanded to include women from across the country who demonstrated an aptitude for math and discretion. These women were ensconced at Arlington Hall, a former girls' school in Virginia, which became the headquarters of the U.S. Army's Signal Intelligence Service (SIS). Codebreaking was excruciatingly complex work and had urgent consequences. Enemy movements were ascertained and ships sunk based on information relayed over the wires. The women were sworn to secrecy about the nature and gravity of their work and for years remained reticent to speak about it, even to family members. Mundy teases out their stories based on extensive interviews with the surviving codebreakers. VERDICT Similar to Nathalia Holt's The Rise of the Rocket Girls and Margot Lee Shetterly's Hidden Figures, this is indispensable and fascinating history. Highly recommended for all readers.--Barrie Olmstead, Sacramento P.L.