A brilliant but troubled neuroscientist working in Prague who has deep ties to secret experiments involving the human mind. In the opening moments, she faces a terrifying interrogation by a monstrous assailant regarding the secrets she and her partners have hidden.

A chilling, clay-covered assailant who models himself after a mythical Jewish creature, believing he is the guardian of a woman named Sasha. He operates as a brutal enforcer targeting those involved with the secret project in Prague, driven by a fractured psyche.

A renowned professor of symbology at Harvard University who is in Prague to support his new romantic partner, Katherine Solomon. At the start of the story, he is enjoying a moment of relaxation at the Four Seasons Hotel before being swept into a dangerous conspiracy.

A prominent noetic scientist and author in Prague to deliver a lecture and publish a book containing explosive scientific discoveries. She has recently begun a romantic relationship with Robert Langdon and is the primary target of an organization desperate to suppress her findings.

The calculating director of a covert organization known as "Threshold," operating deep within the shadows of the intelligence community. He acts as a ruthless guardian of national security who views Katherine Solomon’s upcoming publication as a catastrophic threat.

The United States Ambassador to the Czech Republic, responsible for diplomatic relations and the safety of American citizens in Prague. She leverages her political influence to navigate the crisis when high-profile Americans like Langdon and Solomon are targeted.

A veteran captain with the ÚZSI, the Czech intelligence agency, who is suspicious and hard-nosed. He detains Langdon early in the investigation, believing the American professor may be involved in a security threat or publicity stunt.