Using declassified documents and extensive original research, Secret Pigeon Service tells the dramatic untold story of MI14(d) and its spy networks including the remarkable 'Leopold Vindictive', a Belgian resistance cell who used the pigeon they found in 1941 to spy on the Nazis. Everyone has heard of MI5 and MI6. Some may even have heard of MI9 which helped downed airmen escape in World War II. Few have heard of MI14(d) -- home to Operation Columba.