Top Secret (1967)

A chain of unaccountable disappearances and mysterious murders set in motion a discreet but in-depth investigation by the secret services of Greece. Through a series of seemingly unrelated coincidences, more and more, it becomes evident that the hideous crimes are all connected to the clandestine activity of foreign agents who operate in Greece. Now, some of the government's highly classified documents related to NATO's nuclear experiments become the grand prize for every operative in the business. Will the counter-espionage Operation Hermes bear fruit?