Charles Booth won an Oscar for his writing on this early drama-documentary depicting the hunt by the FBI for an established network of Nazi fifth columnists long since operating in the USA. It falls to agent "Bill Dietrich" (William Eythe) to infiltrate the cell and to find out who is ultimately giving the orders - the mysterious "Mr. Christopher". Reporting to "Insp, Briggs" (Lloyd Nolan) he treads a perilous path as his newfound friends doubt his backstory and suspect him of being a double-agent. I was put off by the overly earnest narrative from Reed Hadley, and the acting is all pretty…