Known as the "Hillbilly Donnie Brasco," FBI agent Scott Payne risked his life to expose violent neo-Nazi cells threatening national security, including the KKK and biker gangs. In 2019, he embedded himself with US extremist groups as part of an FBI investigation to avert a mass shooting planned by a white nationalist group called The Base. Payne talks to Business Insider about undercover protocol, creating legends, whether agents use burner phones, the ethics of undercover work, and surveillance