In 1941 Greece, on the eve of German occupation, cynical American foreign correspondent Michael Morrison arrives in Athens, intending to depart for London the following day. While there he is tricked into smuggling a list of resistance leaders out of the country and is pursued by the Germans.

A team of allied saboteurs are assigned an impossible mission: infiltrate an impregnable Nazi-held island and destroy the two enormous long-range field guns that prevent the rescue of 2,000 trapped British soldiers.