Sophie and Langdon run from the museum and get into Sophie’s tiny car. They head for the embassy. Sophie wonders what the key opens. She thinks about the terrible thing she saw her grandfather doing. Ten years ago, she went to his chateau in Normandy and saw a large group of men and women in a secret room. A ceremony was going on and they were observing something (the reader is not told what). As she is remembering the bizarre and traumatic experience, Sophie stops paying attention the road. She hears sirens and sees that the police have blocked off the street leading to the embassy. When Sophie turns the car around, the police notice and follow her.
Sophie and Langdon continue driving and try to formulate a plan of escape. Langdon looks at the key. Its handle forms a crucifix, a cross with four arms of equal length. Sophie has an idea and drives to the train station. Langdon is apprehensive about her plan and wishes he had turned himself in. They go to the station to buy tickets for the next train out of Paris.
At the airport in Rome, Bishop Aringarosa gets into the car that will take him to Castel Gandolfo, the Pope’s summer residence. He remembers the last time he was at Gandolfo, at a meeting five months ago. On the ride that time, he was thinking about how the current Pope was too liberal, and how ridiculous it was that the Church used Castel Gandolfo, which houses an astronomical observatory, for scientific purposes. Religion and science cannot coexist, he believes. At the meeting, some terrible truth was unveiled. Now, as the Bishop travels to Gandolfo, he wishes the Teacher would call and say that Silas had the keystone.
Sophie and Langdon buy two tickets and get in a waiting taxi. Langdon discovers an address written on the back of the key. They head toward that address.
Fache tells Collet that the train tickets Sophie bought were probably decoys. He decides to alert Interpol to their flight.
While the taxi drives through the Bois de Boulogne, a park full of sexual fetishists and prostitutes, Sophie asks Langdon to tell her about the Priory of Sion. He tells her the brotherhood was established to guard a secret. Its legion of knights found a special cache of documents in a ruined temple. The cache made them rich and famous, but then a pope caused them all to be killed. Since then, the documents have made their way around the globe are now hidden in an unknown place. Langdon tells Sophie that the documents and the secret they corroborate are commonly known as the Holy Grail.