Codes have decided the fates of empires, countries, and monarchies throughout recorded history. Mary, Queen of Scots was put to death by her cousin, Queen Elizabeth, for the high crime of treason after spymaster Sir Francis Walsingham cracked the secret code she used to communicate with her conspirators. And thus the course of British history was altered by a few sheets of cryptic prose. This is just one link in humankind's evolutionary chain of secret communication, and just one of the fascinating incidents recounted in The Code Book, written by bestselling author Simon Singh.

Combining a superb storyteller's sense of drama and a scientist's appreciation for technical perfection, Singh traces the evolution of secret writing from ancient Greek military espionage to the frontiers of computer science. The result is an epic tale of human ingenuity, with examples that range from the poignant to the peculiar to the world-historical.

There is the case of the Beale ciphers, which involves Wild West escapades, a cowboy who amassed a vast fortune, a buried treasure worth $20 million, and a mysterious set of encrypted papers describing its whereabouts--papers that have baffled generations of cryptanalysts and captivated hundreds of treasure hunters.

A speedier end to a bloody war was the only reward that could be promised to the Allied code breakers of World Wars I and II, whose selfless contributions altered the course of history; but few of them lived to receive any credit for their top-secret accomplishments. Among the most moving of these stories is that of the World War II British code breaker Alan Turing, who gave up a brilliant career in mathematics to devote himself to the Allied cause, only to end his years punished by the state for his homosexuality, while his heroism was ignored. No less heroic were the Navajo code talkers, who volunteered without hesitation to risk their lives for the Allied forces in the Japanese theater, where they were routinely mistaken for the enemy.

Interspersed with these gripping stories are clear mathematical, linguistic, and technological demonstrations of codes, as well as illustrations of the remarkable personalities--many courageous, some villainous, and all obsessive--who wrote and broke them.

All roads lead to the present day, in which the possibility of a truly unbreakable code looms large. Singh explores this possibility, and the ramifications of our increasing need for privacy, even as it begins to chafe against the stated mission of the powerful and deeply secretive National Security Agency. Entertaining, compelling, and remarkably far-reaching, this is a book that will forever alter your view of history, what drives it, and how private that e-mail you just sent really is.

Included in the book is a worldwide Cipher Challenge--a $15,000 award will be given by the author to the first reader who cracks the code successfully. Progress toward the solution will be tracked on The Code Book website.