Milan, 1497: Leonardo is completing "The Last Supper". Pope Alexander VI is determined to execute him after realizing that the painting contains clues to a baffling and blasphemous message that he is driven to decode. The Holy Grail and the Eucharistic Bread are missing, there is no meat on the table, and the apostles, shockingly, are portraits of well-known heretics and none of them are depicted with halos. And why has the artist painted himself into the scene with his back turned toward Jesus? The clues to Leonardo's greatest puzzle are right before your eyes.