In 1995, Jostein Gaarder was browsing in an antiquarian bookshop in Buenos Aires, and there, he claims, he came upon a copy of a letter to St. Augustine from his mistress, Floria Aemilia. A true historical figure, Floria was the mother of Augustine's only son. They lived together for over a decade in Africa and then in Italy, until Augustine banished Floria, intending to move on to a socially advantageous marriage. In the end, he never married, choosing instead a path of asceticism.

From her exile, years later, Floria writes the letter that is That Same Flower. Having read Augustine's Confessions and studied philosophy herself, Floria reminds him of their history together. She takes issue with his precepts, especially the redemptive power of abstinence, and defends the pleasures of the senses, pleasures given by God. In many ways a feminist missive, this passionate and occasionally erotic letter questions the Church's view of women and of love.