The Lost Symbol is the third installment in Dan Brown's Robert Langdon series. This conspiracy mystery takes place in Washington, D.C., where Langdon is summoned to give a lecture at the U.S. Capitol. However, he soon finds himself embroiled in a dangerous quest to uncover the hidden secrets of the Freemasons. As Langdon deciphers symbols and navigates through hidden chambers, he races against time to save his mentor and prevent a shocking revelation that could shake the foundations of the United States. The Lost Symbol is a thrilling and thought-provoking novel that explores the power of ancient symbols and the hidden truths they hold.