During the Second World War, Air Commodore Waltby is flying to Allied Command Headquarters with an attaché case packed with information that could stave off an invasion by Germany. Unfortunately, his plane is shot down and he and three colleagues are left drifting in a lifeboat in the North Sea - with the vital intelligence reports still not in the hands of Allied Command. As the Allied authorities direct the search, the four men are edging closer to death and the Germans are planning their assault.