Last fall, the race to stop terrorists from acquiring a nuclear bomb passed through Tashkent, Uzbekistan. There, on the morning of September 19, a Russian Antonov 12 cargo plane touched down carrying two nearly indestructible steel canisters. Under the watch of elite security forces armed with machine guns, Uzbek officials unloaded the canisters and drove them to a remote, wooded area about 20 miles from the Central Asian capital. Waiting there at the Institute of Nuclear Physics, which houses a small nuclear reactor used for scientific research, was a team of Americans, Russians and officials from the International Atomic Energy...