Released in September 2025, this is the sixth Robert Langdon novel and Brown's first in eight years. Langdon travels to Prague with his girlfriend, noetic scientist Katherine Solomon, to attend her lecture on human consciousness — research she's about to publish in a book that threatens to upend established scientific and religious belief. A brutal murder throws the trip into chaos, and Katherine vanishes along with her manuscript. Langdon is targeted by a powerful organization and pursued by a menacing figure drawn from Prague's folklore (a version of the Golem), while local police suspect he and Katherine staged the incident as a publicity stunt. Langdon's investigation leads him through Prague's underground passages to a secret facility, "Threshold," run by a shadowy group with CIA ties, which has been conducting covert research into consciousness, near-death states, and brain-machine interfacing — technology built on ideas the CIA allegedly stole from Katherine's own graduate thesis decades earlier. As with Brown's other Langdon novels, the book is structured as a real-time chase (roughly 24 hours of plot) layered with historical trivia, art and architecture, and puzzle-solving, while raising genuine questions about consciousness research, government secrecy, and the ethical limits of scientific ambition. Critical reception has been mixed: reviewers have praised Brown's ability to make dense scientific ideas accessible and enjoyable, while others found the 650-page length and formulaic structure repetitive for readers already familiar with his previous books.