In 1669, a Parisian bookseller published a slim volume called Portuguese Letters, which unveiled a love affair between a young Portuguese nun and a French officer that had occurred a few years earlier during a war-torn period in Portugal. The book contained passionate love letters from the nun when the officer was forced to return to France. The letters took Paris by storm. They spoke of love in a manner so direct, so precise, and so raw, they sent shivers of recognition through the sophisticated stratums of polite society. Equally remarkable was the mystery that surrounds the letters: the author was unknown, and most people assumed they were the fictional product of a French aristocrat. Now, Myriam Cyr persuasively makes the case that the nun, Mariana Alcoforado, did indeed write the letters, and her story is one of the most moving in the history of forbidden love.