When songwriter Phil Graham is vacationing at a Spanish resort, he runs into old RAF comrade Tony Roscoe, whom he has not seen since the war. Tony is suddenly called back to Britain on emergency business and is not able to drive back to London. Phil volunteers to drive his car back for him and to bring a valuable envelope that Tony has left locked in the hotel safe. After saying goodbye to his old flying buddy, Phil is mugged by thugs while driving Tony's car. Another hotel guest, the enigmatic Mr. Darius, as well as a local police inspector, tell Phil that his old friend has become involved in criminal enterprises since his discharge. When Phil finds him murdered upon returning to Britain, he finds himself in possession of an envelope filled with mysterious microfilm that everyone seems to want.