**Before the multi-million, runaway bestseller The Da Vinci Code , Dan Brown set his razor-sharp research and storytelling skills on the most powerful intelligence organization on earth--the National Security Agency (NSA)--in this thrilling novel, Digital Fortress. ** 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,