Sophie Germain overcame gender stigmas and a lack of formal education to prove that for all prime exponents less than 100 Case I of Fermat's Last Theorem holds. Hidden behind a man's name, her brilliance as mathematician was first discovered by three of the greatest scholars of the eighteenth century, Lagrange, Gauss, and Legendre. In Sophie's Diary, Germain comes to life through a fictionalized journal that intertwines mathematics with historical descriptions of the brutal events that took place in Paris between 1789 and 1793. This format provides a plausible perspective of how a young Sophie could have learned mathematics on her own--both fascinated by numbers and eager to master tough subjects without a teacher's guidance. Her passion for mathematics is integrated into her personal life as an escape from societal outrage. Sophie's Diary is suitable for a variety of readers--both young and old, mathematicians and novices--who will be inspired and enlightened on a field of study made easy, as told through the intellectual and personal struggles of an exceptional young woman.