The story starts with Robert Langdon. He is professor at the University of Harvard. He travelled to Paris to give lectures about his subject; religious iconology.
One night, it’s late and Robert lies in bed. All of a sudden lieutanant Collet comes by. He says that he needs Roberts help on a case.
Robert goes with him to the Louvre Museum, where he meets captain Bezu Fache. The captain walks with him through the museum and then shows him a body. Robert recognizes Jacques Sauniere, the famous Louvre curator. Robert was supposed to meet him earlier that night, but Sauniere never showed up. Now Robert knew why.
His body lied in a strange position.
But what Bezu didn’t tell to Langdon, was that Sauniere wrote Langdons name on the floor. So Bezu thinks that he murdered Jacques Sauniere.
Luckily, Sophie Neveu helps Robert. She is a cryptologist and Sauniere’s granddaughter. Sophie tells Robert that he has a transmitter which tells his exact location to Jacques Sauniere. He throws the transmitter out of the window in a truck, that gives him a more time to take a look at all the hints Sauniere left. It leads them to the painting; The Mona Lisa, Madonna of the Rocks, and finally they find a key. It looks like a key to a vault in a bank.
Robert and Sophie escape from the Louvre. Langdon concludes that Sophies grandfather must be a member of the Priory of Sion, a secret group that protects the secret of the Holy Grail, until the time has come to let the secret out.
The key takes them to a Swedish bank, where they after a lot of trouble manage to enter the vault and get a wooden box with a cryptex in it.
Sophie knows how cryptexes work. Her grandfather used to make them for her. You have to turn the rings untill they form a word, and then you can open it without the contents, which are written on parchment, being destroyed by the breaking of a tube filled with vinegar. If you try to break it with force, they tube will also break and the vinegar will destroy the parchment.
With the police chasing them they go to a friend of Robert called Leigh Teabing. He is an expert on the Holy Grail and the Priory of Sion.
It is a long and interesting story.
In the story, Jesus is described as a man, and not a God. According to the story Jesus and Mary Magdalene were married, and even had children. Teabing shows Sophie a painting of the Last Supper, by Leonardo da Vinci (also a member of the Priory of Sion). It shows that the person sitting on left of Jesus, isn't a man. In fact it is a woman, Mary Magdalene. The Bible says that she is a whore, because Jesus was devine and shouldn’t fall in love like a normal man.
The theory also says that the Holy Grail isn’t a cup; it is a person; Mary Magdalene.
Leigh wasn’t finished with his story but they have to leave. The cops are surrounding the house and a mysterious albino monk attacked them.
With Leighs private jet they fly to London, where they will be safe, and where the Holy Grail should be, according to the legend.
Robert isn’t really safe in England, because Leigh Teabing’s butler turns out to be a traitor and kidnaps Leigh.
Sophie and Robert want to get him back, but for that they must solve the cryptex.
It leads them to Westminster Abbey, to the tomb of Sir Isaac Newton, also a member of the Priory of Sion.
There, they find a note that says to meet Leighs kidnapper somewhere else in the church.
Sophie and Robert decide to go there and find Leigh Teabing, aiming a gun a them and telling them to hand over the cryptex. Sophie and Robert are shocked.
Leigh is convinced the truth about the grail must be shared with the world, and he is willing to do everything for that.
Luckily Robert and Sophie can escape from Leigh and the police captures him. They had come to the conclusion that Robert wasn’t guilty after all.
Robert and Sophie go to the Rosslyn Chapel, where the grail is suppose to be. Sophie had the feeling she had been there before.
They meet a tourguide who tells Sophie he has the exact same wooden box. Sophie says that is impossible because her grandfather made it himself.
Sophie and the tour guide find out that something strange is going on. They both lost their parents and sibling in a car crash when they were very young. The only differences is that Sophie also lost her grandma, and spend her childhood with her grandfather, and that the tour guide lost his grandfather and was brought up by his grandmother.
This couldn’t be coincidence, they are brother and sister.
They go to his grandmothers house and his grandmother immediately recognizes Sophie. She calls her princess, just like her grandfather used to call her.
Sophie finds out the truth about her family. Her mother and father where both from Merovignian families. So she carries the bloodline of Christ. Her parents were killed by a car accident. But Sophie, her brother and grandparents were supposed to be in that car to that same day; only they changed their plans, just before they left.
Sophie is really happy that she found here family, but they still dont know where the Holy Grail is.
He talks about it with Marie, Sophies grandmother, but she tells him to let it rest and that that it will come to him someday.
Weeks later Robert wakes up. He suddenly has the feeling he knows the truth.
The final riddle Sauniere left them was:
The Holy Grail ‘neath ancient Roslin waits.
The blade and chalice guarding Her gates.
Adorned in masters loving art, She lies.
She rests at last beneath the starry skies.
Robert finally understands. Roslina is an old word for Rose Line: The earths original meridian.
It leads Robert through Paris Rue de Rivoli and finally to the Louvre Pyramide. He enters the Louvre and the long tunnel that leads him to La Pyramide Inversee.
Robert realizes he is standing beneath the ancient Rose Line, surrounded by the works of masters.
Now Robert understands the secret. The quest for the Holy Grail is the quest to kneel down before the bones of Mary Magdalene.
And Robert Langdon fell down on his knees.