While Tom Kans, world renowned expert on codes and symbols, is in Paris to give a lecture, he receives a late phone call from the Paris police informing that the manager of the Louvre, Jan Pierre Marie, has been murdered in the famous museum and next to the body the police have found a monogrammed code. Tom is asked to help decipher the code and thus begins a one night adventure, together with Sophie Mone, a leading cryptologist and the niece of the murdered manager, as they follow a series of clues embedded in the art of Leonardo Da Vinci. The mind twisting adventure eventually leads to the Priory of Sion, a secret society whose members included Isaac Newton, Botticelli, Victor Hugo, Da Vinci, as well as Jan Pierre Marie, who, it is discovered, had sacrificed his life to protect the great secret of the Priory: it's the final resting place of the Grail. Pursued by the Paris police and a fanatical assassin of the Opus Dei, Tom and Sophie follow the trail of clues hidden in religious symbols and works of art through London and Paris, finally uncovering the mystery of the Grail. And there's lots of sex too!