FRONTLINE investigates the new nuclear nightmare of the post-Cold War era. While the fear of nuclear annihilation has faded, the security of 1,400 tons of weapons-grade plutonium and highly enriched uranium----enough nuclear material to make roughly 100,000 weapons----is vulnerable to theft in the former Soviet Union. Top American officials call its potential diversion to rogue states or terrorist groups a major threat to U.S. national security. FRONTLINE examines the most serious case of nuclear smuggling in Russia to date and explores the perilous state of nuclear security in a country already rife with chaos and corruption.