This episode dramatises the minute by minute events leading up to the world's first ever atomic bombing. Based on extracts from President Truman's personal diaries which show the decision-making process reflecting America's real fear that the Japanese would never give up, Japanese eyewitness accounts of the tragedy in Hiroshima, diaries written on board Enola Gay, and the personal testimony of Colonel Paul Tibbets, the man who led the mission so secret not even his crew knew the enormity of what they were doing.