The Da Vinci Code

Origin
Dan Brown's The Da Vinci Code is a mystery-detective novel following symbologist Robert Langdon and cryptologist Sophie Neveu.They become involved in a battle between the Priory of Sion and Opus Dei over the possibility of Jesus Christ having been a companion to The Marciana. The title has to do with the first murder victim who was discovered in the Grand Gallery of the Louvre, Paris, naked and posed in the method of Leonardo da Vinci's famous drawing, the Vitruvian Man. Along with that there's a cryptic message written beside his body and a pentagram drawn on his chest in his own blood. The novel explores an alternative religious history, whose central plot point is the Merovingian kings of France being descended from the bloodline of Jesus Christ.

Effects
When left open a light will guide one to the Holy Grail.