Sister Evangeline was just a girl when her father entrusted her to the Franciscan Sisters of Perpetual Adoration in upstate New York. Now, at twenty-three, her discovery of a 1943 letter from the famous philanthropist Abigail Rockefeller to the late mother superior of Saint Rose Convent plunges Evangeline into a secret history that stretches back a thousand years: an ancient conflict between the Society of Angelologists and the monstrously beautiful descendants of angels and humans, the Nephilim.