Summary or teaser for a Robert Langdon novel written by Dan Brown. It appears to describe a plot involving Robert Langdon, a Harvard professor and symbologist, who is drawn into a mysterious and dangerous situation in Washington DC. The story seems to revolve around solving a series of puzzling and potentially deadly clues in order to thwart a sinister plan. The New York Times is quoted praising the story as “impossible to put down” and highlighting it as another captivating addition to the Robert Langdon series. Overall, the story suggests a thrilling and suspenseful narrative involving codes, secrets, and high-stakes intrigue.