The Lost Symbol is the third installment in Dan Brown's Robert Langdon series. This conspiracy mystery novel takes readers on a thrilling journey through the hidden symbols and mysteries of Washington, D.C. Langdon must decipher clues left by a secretive organization known as the Freemasons to save a close friend and uncover a hidden truth that could change the world. The Lost Symbol is a captivating blend of history, symbolism, and suspense that keeps readers guessing until the very end.