In pre-war Germany, a fifth columnist named Karl Ritter is sent by a General of Adolf Hitler on assignment to New England, America, to investigate rumors of a tremendous new factory being built, where the Americans are developing a mysterious new weapon. On arrival he approaches a New England shopkeeper in Lowell City, who tells him that the factory is building Tank Busters. His next mission is to do travel onwards to New York City, and do all that he can to ensure the neutrality of America when the war breaks out...