On July 20, 1944, a German army officer placed a briefcase under a conference table in Hitler's East Prussian headquarters and walked away. The explosion that followed came within inches of killing the Fuhrer and changing history. Claus von Stauffenberg, one-eyed and three-fingered from his wounds in North Africa, was not a revolutionary or a democrat. He was a conservative Catholic aristocrat who had come to believe that the man he had once admired was leading Germany and Europe to catastrophe. The story of Operation Valkyrie is not just the story of one man or one bomb. It is the story of hundreds of soldiers, officials, diplomats, and civilians who organized in secret, risked everything, and ultimately failed — paying with their lives, and with the lives of their families, for their courage. This is the chronicle of what they believed, what they planned, what went wrong on that July afternoon, and how the Nazi regime destroyed them. Operation Valkyrie asks the hardest question in history: when is it right to kill a tyrant? And what does it cost to try?