The never-before-told story of the thrilling hunt for a KGB spy in the top ranks of the CIA, from New York Times best-selling author and former CIA officer Robert Baer.

In the aftermath of the Cold War, American intelligence caught three high-profile Russian spies: Aldrich Ames, Edward Lee Howard, and Robert Hanssen. However, rumors have long swirled of another mole, one perhaps more damaging than all the others combined. Perhaps the greatest traitor in American history, perhaps a Russian ruse to tear the CIA apart, or perhaps nothing more than a bogeyman, he is often referred to as the Fourth Man.

For the first time ever, New York Times best-selling author and former CIA operative Robert Baer tells the full story. After the Ames arrest, the CIA launched another investigation to make sure there wasn't another mole in their ranks. Led by three women, pioneering counterintelligence veterans, its existence was known only to a few. As they hunted through their own, turning up loose threads, smoking guns, and a mercurial KGB source, they came to a startling conclusion that would shake American intelligence to its core. In a cat-and-mouse game worthy of a le Carré novel, the mole hunters squared off against a man who could have been the most damaging spy in US history, a thrilling chase with the profound implications for the future of America, Russia, and the rise of Vladimir Putin.