David Pengelley has recently published an innovative new number theory textbook based on original, historical writings by Sophie Germain, the first woman we know to do important original mathematical research. Readers are guided through primary-source historical documents including excerpts of her own writings, in order to discover, and prove for themselves, many important concepts from introductory number theory. The book is very unusual, combining an inquiry pedagogy with a historical approach to one great problem (Fermat's Last Theorem) based on primary historical sources.