There is no book more exciting to read than one by an author who believes he or she was born to write it. In such books every line becomes a paragraph, every paragraph a chapter, and the book itself a never-ending story. Deborah Hertz's How Jews Became Germans is such a book.

Hertz knew she was onto something big several years before she took pen to paper. While researching her dissertation (a study of late 18th-century Jewish salon women who converted to Protestantism), she discovered the Berlin Jewish Index File, a creation of a Nazi genealogical research project that began in 1933. It presented an apparent comprehensive list of every Jew who converted to Protestantism in Berlin between 1645 and 1933. Once in hand, the Nazis used it to check the ethnic purity of candidates for high positions in the regime, going back at least four generations.