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.