Nuclear weapons never went away when the Cold War ended, and this film argues the danger of their use has actually grown. Director Lucy Walker builds the case through interviews with Robert McNamara, Mikhail Gorbachev, Pervez Musharraf, Valerie Plame, and Pakistani and Russian officials who each handle a different piece of the threat: aging Soviet stockpiles with uncertain security, black-market uranium sales, the shrinking technical gap between a terrorist cell and a working bomb, and the sheer number of false alarms that have almost triggered launches by accident. Archival footage traces the arms race from the Manhattan Project through Hiroshima to the present arsenals still on hair-trigger alert. John F. Kennedy's 1961 UN speech, warning that the world's supply of nuclear weapons put humanity in a countdown, gives the film its title and its throughline. The tone is sober rather than alarmist, laying out a chain of specific failure points, from Pakistan's border security to America's own missile safeguards, and asking what it would actually take to get the number of weapons in the world down to zero.