A 1920s English seaside town bears witness to a dark and absurd scandal: The deeply conservative Edith Swan doesn't have much in common with her neighbor, the rowdy Irish migrant Rose Gooding. When Edith and fellow residents begin to receive wicked letters full of unintentionally hilarious profanities, foul-mouthed Rose is charged with the crime. The anonymous letters prompt a national uproar, and a trial ensues. The town’s women - led by Police Officer Gladys Moss - begin to investigate.