With the Doomsday Clock the closest it's ever been to midnight, Jane Corbin investigates the proliferation of nuclear weapons across the globe. She visits Los Alamos, home to the United States’ nuclear weapons development facility and the historic home of Oppenheimer’s Manhattan Project. In Scotland, she reveals the strategy behind Britain’s nuclear deterrent, and speaks to campaigners in Suffolk fighting against US weapons they fear will be based on UK soil. Jane also discovers how many of the global agreements and safeguards that have constrained the spread of nuclear weapons since the 1970s are breaking down. This is a story told by the scientists, investigators and diplomats who set the clock and have fought to ensure that the ultimate deterrent has not been used in over 70 years.