The Lost Symbol by Dan Brown

The Lost Symbol is a 2009 novel written by American writer Dan Brown. The Lost Symbol is a thriller set in Washington, D.C., after the events of The Da Vinci Code, and relies on Freemasonry for both its recurring theme and its major characters.
Harvard symbologist Robert Langdon is summoned to give a lecture at the United States Capitol, with the invitation apparently from his mentor, a 33rd degree Mason named Peter Solomon, who is the head of the Smithsonian Institution. Solomon has also asked him to bring a small, sealed package which he had entrusted to Langdon years earlier. When Langdon arrives at the Capitol, however, he learns that the invitation he received was not from Solomon, but from Solomon's kidnapper, Mal'akh. Mal'akh then contacts Langdon, charging him with finding both the Mason's Pyramid, which Masons believe is hidden somewhere underground in Washington D.C., and the Lost Word, lest Solomon be executed.
Langdon is then met by Trent Anderson, head of the Capitol police, and Inoue Sato, the head of the CIA's Office of Security. They discover a clue leading to a Solomon's Masonic altar in a room in the Capitol's sub-basement, where they find a small pyramid lacking a capstone, with an inscription. Sato then confronts Langdon with the security x-ray taken of his bag when he entered the Capitol, which reveals a smaller pyramid in the package Langdon brought in response to the request by the kidnapper posing as Solomon. (Summary by Wikipedia)