Subject is exactly extremist groups
The Times published two simultaneous reports of time spent undercover with US Nazi groups in 1937, before World War II. The reporters, brothers John C. and James J. Metcalfe, gained the trust of their "leaders," gaining information deliberately kept out of the public sphere by the group. The reports are accompanied by stories about events in Germany, nazi action in the US, and results of the Times reports themselves. Everything's published here in the original page layout, with multiple stories per entry.
John Ray Carlson is the pen name for Avedis Boghos Derounian. His book, "Under Cover," and the American Mercury article "Our Fascist Enemies Within" were based on extensive research, a lot of it under cover, with a number of nazi sympathetic groups in the U.S.
A collection of undercover reportages focused on ideological and religious groups generally hidden from the public eye.