During the Vatican’s papal conclave of 1740, violinist Antonio Vivaldi is given a devastating secret by his dying mentor, Cardinal Pietro Ottoboni, the man favored to be elected Pope before he was poisoned. Fearful of the Italian Camorra, Vivaldi hides the secret in a special cipher in his music—a cipher revealing a breathtaking centuries-long operation of art theft from the Vatican Museum and forgery of its priceless paintings.

Almost three hundred years later, the encoded music is discovered by Father Michael Dominic, Prefect of the Vatican Secret Archive, who tries decoding the cipher with the help of journalist Hana Sinclair and her former teacher, music cryptologist Dr. Livia Gallo. Dominic, Hana, and their Swiss Guard companions Karl Dengler and Lukas Bischoff, meet up in the enchanted city of Venice during Carnivale celebrations to further investigate Vivaldi’s coded music with the help of the maestro’s descendant, Contessa Donatella Vivaldi—whose palazzo on the Grand Canal holds many secrets of its own.

The notorious Italian Mafia organization known as the Camorra tries everything in its power to stop Dominic and his friends from digging deeper into their secret forgery operation. But now Dominic and his team are joined by former French commando Marco Picard, whose tactics are a stubborn match for the brutal ways of the Camorra.