1920: The slaughter of World War I was over, but already secret little wars were breaking out all over the "New Europe." Sub-Lieutenant de Vere Smith V.C. is asked by the head of the Secret Service if he will help to convoy arms to the Poles. He jumps at the chance, refitting his old fast patrol boat and sets off for the Baltic. But secret enemy forces are everywhere, trying to stop the "Swordfish" from fulfilling its mission.