Amid the nuclear threat of the Cold War, America's prized secrets were falling into the hands of its sworn enemy. The FBI's hunt for the leak led to an astonishing discovery—the mole was one of its own, special agent Robert Hanssen. For two decades, Hanssen masqueraded as a devoted patriot while ruthlessly selling out his country, trading classified intelligence to the Soviet Union and later Russia, in exchange for cash and diamonds. He was a whirlwind of contradictions—a self-proclaimed patriot and a traitor; a family man who sexually betrayed his wife; an ardent man of God and a...