Langdon figures out this final piece to the puzzle; he follows the Rose Line to La Pyramide Inversée, where he kneels before the hidden sarcophagus of Mary Magdalene, as the Templar knights did before him.
Langdon figures out this final piece to the puzzle in the last pages of the book but he does not appear inclined to tell anyone about this. He follows the Rose Line to La Pyramide Inversée, where he kneels before the hidden sarcophagus of Mary Magdalene, as the Templar knights did before him.