In the small town of Harper, Connecticut, a stranger named Mr. Wilson (Edward G. Robinson) arrives on the day of the wedding of Mary Longstreet (Loretta Young) to Professor Charles Rankin (Orson Welles). But all is not what it seems, as Mr. Wilson is an investigator for the Allied War Crimes Commission following concentration camp commandant Konrad Meinike (Konstantin Shayne). He, in turn, is seeking a notorious Nazi named Franz Kindler, architect of the mass murder of millions during the Second World War and living somewhere in Harper.