Spy and art restorer Gabriel Allon is in Venice repairing an altarpiece when he receives a summons from the Italian police. London art dealer Julian Isherwood has stumbled upon a chilling murder scene in Lake Como, and is being held as a suspect. To save his friend, Gabriel must track down the real killers and then perform one simple task: find the most famous missing painting in the world. The dead man is a fallen British spy with a secret: he has been trafficking in stolen artworks and selling them to a mysterious collector. Gabriel embarks on a daring gambit to recover it and learn the identity of the collector.