Hubert Wolf is a distinguished German ecclesiastical historian whose study of the nuns of Sant’Ambrogio was first published in German in 2013. It has been quickly translated and it is easy to see why. Based on a file of inquisitional reports that had lain concealed in the Vatican archive for a century and a half, the book tells a riveting tale of sex and religion. The immediate setting is a building which a pertinacious visitor can still locate in Rome near the Tiber and the Ghetto. Back in the 1850s it housed the enclosed nuns of the Regulated Third Order of Holy Saint Francis, governed by a severe rule that their founder, Maria Agnese Firrao, had established with the help of her confessor in 1806.