In the nuclear age, arms are the ultimate commodity. And now they are easier and cheaper to acquire and make than ever before - which means that for poor nations or non-state terror groups, weapons of mass destruction are up for grabs. William Langewiesche looks at how nuclear weapons have gone wholesale. He visits the smuggling routes in Turkey and closed Russian 'nuclear cities' where highly enriched uranium is on sale. He meets technicians, smugglers and spies. And he tells the extraordinary story of Abdul Qadeer Khan, the scientist who stole plans to build Pakistan's nuclear arsenal.