Chapter 21
Chapter Characters:
Robert Langdon
Sophie Neveu

Chapter Summary:
Sophie recalls that her grandfather, when young, created anagrams of works of art. He introduced her to the Mona Lisa when she was six years old, and she thinks a clue might be there. She decides to go back to the Mona Lisa while Langdon goes to the U.S. Embassy. They part and Langdon starts to leave the Louvre. He realizes there is more to the code and races back to join Sophie.

Chapter Themes:
The human world is encoded with meaning.
The centrality of human relationships, especially male-female relationships.
The influence of the past upon the present.

Chapter 22
Chapter Characters:
Bishop Aringarosa
Silas, the albino monk

Chapter Summary:
In the Church of Saint-Sulpice, Silas pretends to pray, then follows the Rose Line, a strip of brass embedded in the stone floor, to the keystone. "'And so the legend is true,' the Teacher had told Silas. 'The Priory keystone has been said to lie "beneath the Sign of the Rose."'" The brass strip is a gnomen—a pre-Christian astronomical device similar to a sundial. It cuts the church in half, ending at an obelisk. The brass marker is a memorial to the original zero-longitude line that passed through Paris before being moved to Greenwich, England.

The symbol of the Rose has for centuries been tied to maps. The Compass Rose on a map was originally known as the Wind Rose. It marked the directions of thirty-two winds, with the points resembling the thirty-two petals of a rose. The symbol of the fleur-de-lis marks the north direction on a Compass Rose.

As Silas searches, Aringarosa arrives in Rome.

Chapter Themes:
The human world is encoded with meaning.
The centrality of human relationships, especially male-female relationships.
The power of belief, and the need to believe.
The influence of the past upon the present.

Chapter 23
Chapter Characters:
Robert Langdon
Sophie Neveu

Chapter Summary:
Sophie goes to the room that houses the Mona Lisa after retrieving a black-light pen from the crime scene. There she finds Langdon, who asks her if the letters P.S. mean anything else to her.

Sophie remembers prying into her grandfather's secrets without invitation when she was nine years old, and the coded treasure hunts he used to set up for her. While searching for hidden birthday presents, she found a gold necklace and key embossed with the letters P.S. and a fleur-de-lis. Her grandfather said the key opened a box that held his secrets; if she kept the key a secret, one day he would give it to her. He told her P.S. was a code for her secret initials. This reveals the origin of the initials P.S. for Princess Sophie. The initials also refer to the Priory of Sion (in French, the Prieuré de Sion), a secret society with pagan roots, which Langdon recognizes. He is convinced Saunière belonged to the Priory of Sion because the fleur-de-lis and the initials P.S. are their symbols. Langdon tells Sophie that the Priory of Sion is known to be the guardian of an ancient secret that has made them very powerful.

Across Paris, the police find the bugged bar of soap.

Chapter Themes:
The human world is encoded with meaning.
The centrality of human relationships, especially male-female relationships.
The influence of the past upon the present.

Chapter 24
Chapter Characters:
Sister Sandrine
Silas, the albino monk

Chapter Summary:
Back in the Church of Saint-Sulpice, Silas looks for something to break the floor stone. As he does so, the watching Sister Sandrine realizes what he is looking for.

Chapter Themes:
The human world is encoded with meaning.
The centrality of human relationships, especially male-female relationships.
The power of belief, and the need to believe.

Chapter 25
Chapter Characters:
Bezu Fache

Chapter Summary:
Fache calls the U.S. Embassy, pretending to be Langdon in order to access Langdon's phone messages. Fache finds that the earlier message for Langdon was not from the embassy. Realizing Langdon had used Fache's phone to place his call, Fache redials the last number dialed. He reaches Sophie's number and hears the message Langdon had heard.

Chapter Themes:
The human world is encoded with meaning.
The influence of the past upon the present.

Chapter 26
Chapter Characters:
Robert Langdon
Sophie Neveu

Chapter Summary:
As Langdon and Sophie approach the Mona Lisa, Langdon recalls lecturing to convicts about Mona Lisa's secret. He showed them the uneven background of the painting, with the lower horizon line on the left making Mona Lisa look grander from that side. The female, which Da Vinci admired, is historically associated with the left side. But Da Vinci believed in the balance between male and female, and the origin meaning of the painting's name—Amon (Egyptian god of fertility) and Isis (goddess of fertility)—was DaVinci's clue that the painting is androgynous: "'Not only does the face of Mona Lisa look androgynous, but her name is an anagram of the diving union of male and female. And that … is Da Vinci's little secret, and the reason for Mona Lisa's knowing smile."

At the Mona Lisa, they find a six-word message in black-light pen, written across the painting's protective glass.

Chapter Themes:
The human world is encoded with meaning.
The centrality of human relationships, especially male-female relationships.
The power of belief, and the need to believe.
The influence of the past upon the present.

Chapter 27
Chapter Characters:
Bezu Fache
Jérome Collet

Chapter Summary:
Fache and Collet reason through the fact that Sophie is still in the Louvre with Langdon, and Fache sets men to capture them.

Chapter 28
Chapter Characters:
Robert Langdon
Sophie Neveu

Chapter Summary:
Langdon and Sophie read the message on the Mona Lisa: "So Dark the Con of Man," which Langdon interprets as meaning early Christians devaluing the feminine a "con" or deception—a Priory of Sion belief that perpetuates their goddess worship. The message is proof to Langdon that Saunière was a member of the Priory.

A Louvre security guard bursts in and captures Langdon.

Chapter Themes:
The human world is encoded with meaning.
The centrality of human relationships, especially male-female relationships.
The power of belief, and the need to believe.
The influence of the past upon the present.

Chapter 29
Chapter Characters:
Sister Sandrine
Silas, the albino monk

Chapter Summary:
In the Church of Saint-Sulpice, Silas breaks the stone panel open and pulls out the keystone, finding a reference to the Bible verse Job 38:11, "Hitherto shalt thou come, but no further," which is meant to signify the fact that this is a dead end: a false keystone.

Sister Sandrine rushes to her quarters and retrieves a long-hidden envelope in which she finds four Paris phone numbers. She dials the numbers to sound an alert.

Chapter Themes:
The human world is encoded with meaning.
The centrality of human relationships, especially male-female relationships.
The power of belief, and the need to believe.
The influence of the past upon the present.

Chapter 30
Chapter Characters:
Claude Grouard
Robert Langdon
Sophie Neveu

Chapter Summary:
The Louvre security guard, Claude Grouard, wants to kill Langdon for killing Saunière. Sophie confronts him and says Langdon did not kill Saunière. Grouard repeatedly calls for backup, but he only hears static on his radio.

Meanwhile, Sophie searches another Da Vinci painting nearby, finding a key hidden there—the gold key she had found years ago in her grandfather's bedroom. Sophie hides behind the Da Vinci painting, essentially holding it hostage.

Once she and Langdon are past Grouard, Sophie explains that "so dark the con of man" is another anagram, this one for "Madonna of the Rocks," the Da Vinci painting that Sophie had been holding hostage.

Chapter Themes:
The human world is encoded with meaning.
The centrality of human relationships, especially male-female relationships.
The power of belief, and the need to believe.
The influence of the past upon the present.