When Cliff Stoll followed the trail of a 75-cent accounting error at his workplace, the Lawrence Berkeley National Laboratory, it led him to the presence of an unauthorized user on the system. Suddenly, Stoll found himself crossing paths with a hacker named "Hunter" who had managed to break into sensitive United States networks and steal vital information.

Stoll made the dangerous decision to begin a one-man hunt of his own: spying on the spy. It was a high-stakes game of deception, broken codes, satellites, and missile bases, one that eventually gained the attention of the CIA. What started as simply observing soon became a game of cat and mouse that ultimately reached all the way to the KGB.