The Secret of Secrets

The Secret of Secrets (2025) is the sixth novel in the Robert Langdon series written by best-selling American author Dan Brown. The novel follows Harvard symbologist Langdon and his longtime friend and love interest, Katherine Solomon, as they fight against a CIA plot to sabotage the publication of Solomon’s newest book. Langdon’s historical knowledge and Solomon’s research in human cognition enable them to uncover an experimental program with world-changing implications. Major themes in the book include The Dangers and Limits of Technology, The Ethics of National Security, and The Nature of Human Consciousness.

This guide is based on the 2025 Doubleday e-book edition.

Content Warning: The source material and guide feature depictions of death, emotional abuse, physical abuse, ableism, substance use, and cursing.

Plot Summary

In Prague, neuroscientist Dr. Brigita Gessner is tortured in her underground laboratory by a mysterious figure caked in mud called the Golem. She admits to horrific acts committed there by her team of scientists on human test subjects. The Golem kills Gessner and swears vengeance on behalf of an unnamed woman.

Meanwhile, also in Prague, Robert Langdon attends Katherine Solomon’s lecture on her new book, which will revolutionize noetic science (the study of consciousness). That night, Solomon has a nightmare about a woman wearing a spiked crown warning of an explosion at their hotel. While running the next morning, Langdon sees the woman on the Charles Bridge and panics. When he cannot find Solomon in their room, he pulls a fire alarm to evacuate the hotel. It does not explode, but Langdon is shocked to learn that police did in fact diffuse a bomb at the hotel that morning. Langdon shares his dream with Captain Oldřich Janáček, who accuses him and Solomon of staging the bomb threat for publicity for Solomon’s book, which argues for the possibility of precognition.

Solomon’s book manuscript is deleted from the press’s secure servers hours after being delivered to her editor, Jonas Faukman, and Faukman is kidnapped when he leaves his office to digitize the sole printed copy of the manuscript. The kidnappers destroy the manuscript. In London, CIA agent Everett Finch panics when he cannot contact Gessner and orders field agents from an organization called “Q” to execute missions for a project called Threshold.

Janáček and his lieutenant, Pavel, bring Langdon to Brigita Gessner’s institute in Prague, where Solomon has scheduled a meeting. Langdon manages to escape into a hidden elevator in the lobby. In the basement of the facility, he finds a body inside a mechanical pod. Gessner’s lab assistant, Sasha Vesna, appears and opens the pod, revealing Gessner’s corpse. Vesna explains that she is receiving seizure treatment invented by Gessner through an implant in her forehead that is activated by a “metal wand.”

Meanwhile, Janáček receives a call from the American ambassador, which reveals he lied about the presence of a bomb at Langdon’s hotel. Shortly after, he is pushed off a steep cliff by the Golem. Inside Gessner’s facility, Vesna and Langdon knock out Pavel and escape from into Folimanka Park, followed from a distance by the Golem.

American ambassador Heide Nagel orders embassy staff member Michael Harris to give Q agent Susan Housemore access to Langdon and Solomon’s suite. It is revealed that Finch bugged Langdon’s suite to discover information about Solomon’s work.

Vesna takes Langdon to her apartment to wait for Harris, whom she believes is her boyfriend but who has actually been spying on her for Nagel. Shortly after arriving, they find a note from the Golem claiming to have Solomon at the Petřín Tower. When Langdon leaves, the Golem renders Vesna unconscious and waits for Harris, killing him on arrival. It is revealed that the Golem has the same implant as Vesna, controlling his epilepsy with a metal wand, and that she is the woman he has dedicated his life to protecting.

Langdon is recognized by his taxi driver, who reports his location following an emergency alert organized by Pavel. He finds no one at the tower, but receives an email from Katherine containing a phrase in the mystical Enochian language. He realizes that Katherine’s message refers to a famous bible they had seen at the Klementinum Library the previous day.

In New York, Solomon stages an escape, unaware that the kidnappers allowed him to escape after bugging his phone and the van he stole. Back the Random House offices, security tech Alex Conan is about to reveal who hacked the manuscript when Faukman realizes the men have followed him into the building. He bluffs, identifying the hacker as a rival publisher. The kidnappers are intercepted by Random House security as they try to leave.

Pavel follows Langdon to the Klementinum Library, hoping to avenge Janáček personally. Inside, Langdon finds Solomon hiding in a secret passage he had shown her the previous day. Pavel attempts to break in, but Langdon starts a fire with the sole remaining copy of Solomon’s manuscript, leading Library staff to intervene. Pavel is detained by Dana Daněk, sent by the Ambassador to collect Langdon and Solomon. On the way, Solomon reveals her bombshell research, which suggests the neurochemical GABA filters the full spectrum of consciousness to suit the human brain.

Ambassador Nagel asks Langdon and Solomon to sign an NDA before speaking to Finch personally about why their hotel room was bugged. They refuse. Langdon calls Faukman and learns that the hack was orchestrated by In-Q-Tel (also known as Q), a real-life venture capital firm funded by the CIA. News of Michael Harris’s death leads Nagel to reveal the truth: Solomon’s research poses a threat to one of Q’s primary investments, a research facility codenamed Threshold. Langdon convinces Nagel to help him and Solomon infiltrate Threshold and obtain hard evidence. A letter addressed to Nagel is found on Harris’s body, directing Nagel to an online recording of Gessner being tortured by the Golem and admitting the details of Threshold. Furious, Nagel saves several copies and forwards the link to the CIA Director Gregory Judd with a list of demands.

Langdon and Solomon return to the Gessner Lab, which Langdon believes is a second entrance to Threshold. Unbeknownst to them, the Golem has also infiltrated the Gessner lab in hopes of destroying it. As they explore, Solomon theorizes that the purpose of Threshold is to design and install chips enabling subjects to experience nonlocal consciousness. She discovers proof that Threshold scientists have grown artificial neurons using a process she proposed in graduate school two decades earlier.

Finch learns of Nagel’s call to CIA Director Judd and decides to go to the Gessner Lab personally. He discovers Gessner’s body and a metal wand, and theorizes that she was killed by either Sasha Vesna or a patient named Dmitri Sysevich, the only other patient with the epilepsy implant. At the edges of the Threshold facility, the Golem finds a giant silo containing the superconducting magnetic energy storage machine that powers the project, and prepares to destroy it. The resulting explosion would destroy the facility. Langdon and Solomon accidentally close the escape route, unwittingly locking themselves inside a ticking time bomb.

Finch eventually discovers Langdon and Solomon and holds them at gunpoint. He confirms that the goal of Threshold is to create psychic superspies capable of observing enemies remotely. The Golem interrupts Finch with a stun gun and locks him inside one of the facility’s pods. Finch dies instantly as the facility explodes. Langdon and Solomon make it to the facility’s edge, but are locked out of escape at the last moment. They survive and are rescued from military detainment by Nagel’s Marine guard Scott Kerble. Langdon convinces Kerble to take them to Sasha Vesna’s apartment, where they discover a passageway to a second apartment. They find a used bald cap with a blond hair inside.

The Golem also survives the blast, escaping back up to the Gessner Labs and removing his disguise, revealing the body of Sasha Vesna. It is revealed that the Golem is an alternate identity created by Vesna’s consciousness to protect her during years of abuse in the Russian mental institute. Langdon and Solomon, who have realized the truth, share the news with Ambassador Nagel.

Vesna appears at the embassy asking for asylum. Nagel argues that the best place for Vesna is with CIA doctors, who can care for and protect her, with Nagel holding the Gessner tapes as leverage. Langdon agrees to help convince Vesna, obtaining consent from her alternate identity. Ambassador Nagel arranges for Vesna to be taken to America. Before leaving Prague, Langdon reveals that he only burned Solomon’s bibliography, and that the rest of the book manuscript survived.