"Mud angels" is what the Italians call the selfless young foreigners who come to Florence in 1966 to save the city's priceless art from the Arno's flooded riverbanks.

Margot Harrington is an American volunteer, an expert at book conservancy. While struggling to save a waterlogged convent library, she discovers a fabulous volume of sixteen erotic drawings by Giulio Romano that accompany sixteen steamy sonnets by Pietro Aretino. When published more than four centuries earlier, the Vatican had insisted all copies be destroyed. This one - now unique - volume has survived.

The abbess, with wonderful aplomb, prevails upon Margot to save the order's finances by selling the magnificently illustrated erotica, discreetly. Meaning: without the bishop's knowledge. The young American's other clandestine project is a middle-aged Italian who is boldly trying radical measures to save endangered frescoes. She is 29 and available; he, older and married. He shares her sense of mission and then her bed in this ambrosial story of spiritual longing and earthly desire.