As Silas arrives at Saint-Sulpice, he reflects on his past. He ran away from home at a young age after murdering his abusive father and continued to live a life of violence. He was in prison for murder when an earthquake opened a big hole in the wall of his cell. When he ran, he ended up at a church in Oviedo, Spain. Aringarosa, then a missionary, saved him and gave him the name Silas, after a passage in the Bible. From that point on Silas became deeply devout. He is now Aringarosa’s faithful righthand man.
On the plane, Bishop Aringarosa thinks about how Opus Dei offered the Teacher a large amount of money for information about the location of the keystone. The Teacher told Aringarosa that he must not be in contact with Silas, presumably in order to maintain secrecy and throw the police off the scent.
As Langdon listens to Sophie’s message, Sophie tells Fache that if put in ascending order, the numbers next to Saunière’s body form the Fibonacci sequence, a progression in which each term is equal to the sum of the two preceding terms. If Sophie is right, the code was a cryptographic joke. Unsatisfied with Sophie’s interpretation, Fache grows even angrier. Sophie leaves, and Langdon tells Fache that according to the embassy, a friend has had an accident. Langdon goes to the restroom after saying he isn’t feeling well and would like to be alone. Collet and Fache track him electronically. Fache tells Collet to make sure Langdon doesn’t leave the gallery.
Sophie meets Langdon in the bathroom to explain her message further. She tells him that he is a suspect, and that a GPS tracker has been planted on him. After rummaging in his pocket, Langdon finds a tracker and realizes it must have been planted on him at the hotel. Langdon’s first impulse is to throw the tracker away, but Sophie convinces him that a static dot on the tracking screen would immediately arouse police suspicion. She shows him a picture of the crime scene that Fache uploaded to her departmental website. Fache photographed a line and then erased before Langdon’s arrival, but the line is visible in the picture. It reads, “P.S. Find Robert Langdon.”
Sophie tells Langdon that the police have more than enough evidence to arrest him for the murder, but she knows that he is innocent. She believes Saunière was telling her to look for him. Saunière knew that The Vitruvian Man was her favorite Da Vinci drawing. He also must have known that if he put numbers into the message on the floor, the cryptography department would get involved with the investigation. Also, she thinks that the “P.S.” in the message “P.S. Find Robert Langdon” stands for Princesse Sophie, his nickname for her. Langdon is confused about Sophie’s connection to Saunière. He suspects that Sophie may have been Saunière’s mistress until she tells him that Saunière was her grandfather, but that they’d had a falling-out.