Sobel bases her book on 124 surviving letters to the scientist from the nun, whom Galileo described as "a woman of exquisite mind, singular goodness, and tenderly attached to me." Their loving correspondence revealed much about their world: the agonies of the bubonic plague, the hardships of monastic life, even Galileo's occasional forgetfulness ("The little basket, which I sent you recently with several pastries, is not mine, and therefore I wish you to return it to me").

First published in the United States by Walker, 1999.