Producer David Goren has the story of a mystery on shortwave radio. There are a number of stations which transmit nothing but numbers — a series of numbers, read by an unidentified voice, all day, every day. We hear from several shortwave enthusiasts, and experts on international espionage, who believe that the numbers are encrypted code, delivered by government intelligence agencies to spies around the world. It is a mystery where the transmission come from, and who they are meant for. We hear the transmission of these "number stations" from the CIA , western European countries, and Russia. After the Cold War, many of the transmissions that were originating from Communist countries stopped. Many number stations today can be linked with Cuba, China, and Taiwan. Shortwave experts and code experts continue to be fascinated by the number stations — the notion that what is coming out of your radio is meant for one person only, in a coded language only he can understand.