Sophie's Diary: A Mathematical Novel is a work of fiction inspired by French mathematician Sophie Germain. It chronicles the coming of age of a teenager learning mathematics on her own, growing up during the most turbulent years of the French Revolution. The fictionalized diary uses mathematics, intertwined with historically-accurate accounts of the social chaos that reigned in Paris between 1789 and 1794, to describe the learning journey of a remarkable girl that became the first and only woman in history to make a substantial contribution to the proof of Fermat’s Last Theorem. Sophie Germain was born in Paris in 1776. Little is known about her childhood or about her initiation into mathematics. Her first biographers wrote that, as a young woman, she assumed the name of a male student at the Ecole Polytechnique to submit her own work to Lagrange. Yet, no biography has explained how Germain studied mathematics before that time to encourage such boldness. Sophie's Diary is an attempt to put in perspective how a self-taught girl could have acquired the knowledge to enter the world of Lagrange's analysis.