Admirers and detractors use the same words to describe Jessica Mitford: subversive, muckraker, mischief-maker. But those who knew her best simply called her Decca. Born into one of Britain's most famous aristocratic families, at the age of nineteen she ran away with Winston Churchill's nephew. Their elopement severed ties with her privilege, a rupture only exacerbated by the controversial life she would go on to lead for seventy-eight years.

Decca arrived in the United States in 1939, and before long became one of the New Deal's most notorious bureaucrats. She went on to work as a civil...