The monastery of San Giovanni has few treasures -- only a painting doubtfully attributed to Caravaggio. So Flavia di Stefano of Rome's Art Squad is surprised to receive a tip-off that a raid is being planned. The raid happens, but the thieves are disturbed and snatch the wrong painting, a curious icon of the Madonna, remarkable only for the affection in which it is held by the local population. Or is this what the thieves wanted all along? Does the legend of the icon's miraculous powers hold any clue? And who murdered the French dealer found in the Tiber soon afterwards? Flavia, with the help of English art dealer Jonathan Argyll, immerses herself in the intricacies and intrigues of monastic and police politics in an attempt to solve the double mystery, but the solution that awaits her is murkier and more complex than anyone could have known.