It's 1931 and Nancy Mitford introduces her six innocent-seeming siblings at a pool party, but warns everyone about how notorious they will become, and Diana soon starts to fall for Oswald Mosley.

Diana's affair with Mosley makes newspaper headlines. Unity also embraces fascism, while Jessica is drawn to communism. Nancy is heartbroken but then receives a surprise proposal.

Nancy writes a novel spoofing the Blackshirts which angers Diana, Jessica becomes obsessed with her communist cousin Esmond, and Unity goes to Munich, hoping to meet Hitler.

Unity finally meets Hitler and embraces Nazi views, appalling her family. Debo falls in love with an older man and, after a row with Nancy, Diana drives furiously into the night.

Diana recovers from her crash in Italy with Mosley, Unity is befriended by Hitler, Jessica's obsession with Esmond grows, and Nancy hopes her husband has turned over a new leaf.

Diana and Mosley secretly marry, Pam announces her engagement, Jessica finally meets Esmond, and a family reunion goes awry thanks to Nancy.