The central mystery in "The Da Vinci Code" revolves around the interpretation of a cryptic message left by Leonardo da Vinci, which leads Langdon and Neveu on a quest to uncover the location of the Holy Grail.

The dark secret in "And Then There Were None" is that each of the guests on the island has committed a murder in the past, and they are brought together to face the consequences of their actions.

The shocking revelation in "Gone Girl" is that Amy's disappearance was not a genuine kidnapping, but rather a meticulously planned scheme to frame her husband and seek revenge.

The mole within the British Secret Service in "Tinker Tailor Soldier Spy" is revealed to be Bill Haydon, a high-ranking official who has been secretly working for the Soviet Union.

In "1984", the totalitarian government that controls Oceania is simply referred to as "The Party", which exercises absolute power and surveillance over its citizens.

The central mystery in "The Girl with the Dragon Tattoo" is the disappearance of Harriet Vanger, a wealthy family's daughter, which Blomkvist and Salander investigate to uncover the dark secrets of the Vanger family.

Jason Bourne's secret past in "The Bourne Identity" is that he is a former assassin trained by a secret government agency, known as Treadstone, and he is trying to regain his memory and uncover the truth about his past.

Woodward and Bernstein uncover a cover-up of illegal activities within the White House, including the break-in at the Democratic National Committee headquarters, which eventually leads to the resignation of President Nixon.

Mitch McDeere discovers that the prestigious law firm he joins, Bendini, Lambert & Locke, is involved in money laundering for a powerful crime syndicate, and he becomes entangled in a dangerous web of corruption and deceit.

The mental institution in "Shutter Island" is revealed to be a secret government facility where experiments are conducted on mental patients, and Teddy Daniels is unknowingly part of a psychological experiment.

Hannibal Lecter and Clarice Starling share a connection as brilliant minds with a deep understanding of human behavior, which allows them to communicate and engage in psychological battles despite their adversarial positions.

The secret plot in "The Manchurian Candidate" involves a foreign government implanting sleeper agents in the American military through brainwashing techniques, with the aim of controlling the United States government.

George Smiley is the top agent of the British Secret Service who is tasked with uncovering a mole within the organization, as depicted in the novel and its adaptations.

The narrator and Tyler Durden are revealed to be two sides of the same person, representing different aspects of his psyche, as the narrator struggles with his own identity and mental state.

The secret government program that trained Jason Bourne as an assassin in "The Bourne Identity" is known as Treadstone.