Digital Fortress is a techno-thriller novel written by American author Dan Brown. The book explores the theme of government surveillance of electronically stored information on the private lives of citizens, and the possible civil liberties and ethical implications of using such technology.

When the NSA's invincible code-breaking machine encounters a mysterious code it cannot break, the agency calls its head cryptographer, Susan Fletcher, a brilliant, beautiful mathematician. What she uncovers sends shock waves through the corridors of power. The NSA is being held hostage—not by guns or bombs—but by a code so complex that if released would cripple U.S. intelligence.

Caught in an accelerating tempest of secrecy and lies, Fletcher battles to save the agency she believes in. Betrayed on all sides, she finds herself fighting not only for her country but for her life, and in the end, for the life of the man she loves.

George Hartley wakes up and realizes that he’s lost his memory. He sees a dead woman sitting in a wheelchair. George searches the place and finds himself trapped in a skyscraper. Someone left the documents revealing that his ex-colleagues, financial partners, and even intelligence officers had been spying on him, watching his business activity, digging up dirt on him, and someone must have poisoned him. Numerous facts show that George Hartley was one of the most influential investors and traders in London. He was the head of the largest British financial fund.

All of a sudden, his enemies make an attempt to kill him, and George Hartley barely escapes the skyscraper. He shakes off the pursuers, finds a temporary hideout, and continues to collect the information on his life. Soon, George finds out that for many years, he has been engaged in high-level behind-the-scenes machinations as a creator and manipulator of future financial developments, events, international scandals, information wars that affected stock and commodity markets’ prices. For the past several months, he met North Korean leader and convinced him to launch a missile, conducted an operation against Saudi Arabian Oil Company, and set off a panic in the oil market, held a secret meeting with a Russian oligarch to speculate on sanctions against Russia. The more facts George Hartley finds out, the more he realizes he misled and deceived thousands of traders and investors, and probably bankrupted them. He hates his past and wants to start a new life.

But his ex-colleagues and enemies don’t let him leave the game. They start using him as a money-making machine, trading and manipulating his life and death. George Hartley has nothing to do but to declare financial war against them.