Harvard professor Robert Langdon receives an urgent late-night phone call while on business in Paris. The elderly curator of the Louvre has been found murdered inside the museum, his body surrounded by a series of bizarre ciphers scribbled in invisible ink. As Langdon and a gifted young French cryptologist, Sophie Neveu, attempt to make sense of the chilling clues left around the body, they are stunned to realize the riddles are connected to the works of Da Vinci and may be linked to a mystery that stretches deep into the history of the Catholic Church.

Langdon learns the late curator was the gatekeeper of the Priory of Sion — an actual secret society whose members included Sir Isaac Newton, Botticelli, Victor Hugo, and Da Vinci — and has sacrificed his life to protect the Priory's most sacred trust, the location of a vastly important religious relic hidden for centuries. It appears that Opus Dei, a clandestine,  Vatican-sanctioned religious sect that has long plotted to seize the Priory's secret, has now made its move.

The plot continues in ways that combine the detective thriller and conspiracy theory genres with Saunière's murder being attributed to powerful forces that wish to preserve ancient secrets relating to Jesus having been married to Mary Magdalene and having been the father of their child. The interpretation of hidden messages inside Da Vinci's famous works, including the Mona Lisa and The Last Supper, figure prominently in the solution to the mystery. The solution itself is found to be intimately connected with the possible location of the Holy Grail and to a mysterious society called the Priory of Sion, as well as to the Knights Templar.  Unless Langdon and Neveu can decipher the labyrinthine code and quickly assemble the pieces of the puzzle, the Priory's secret - and a stunning historical truth - will be lost for ever . . .