Learning the nature of nuclear materials and their locations often takes months of diplomacy. In Kazakhstan, shortly after the fall of the Soviet Union, I had to go on a moose-hunting trip in the Altai Mountains with Vitaly Mette, the director of a factory where fissile material was stored. I bonded with him in naked bathhouse sessions and over shots of Wild Turkey whiskey. Weeks later, after I had gained Vitaly’s trust, a burly former K.G.B. colonel took me for a walk in a snowy courtyard outside Almaty; he passed me a note from Vitaly that read, “U 235, 90%, 600 kg.” This meant that Vitaly had a cache of uranium, highly enriched to 90 percent concentration of its highly fissionable element — sufficient for about two dozen nuclear weapons.