On the day she was murdered, Myrtle Underwood Cook boasted to local authorities about new evidence of a major bootlegging ring operating out of the Rock Island train depot behind her house in a small town in eastern Iowa. Then, as she sat at her window sewing, she took a single slug through the heart. She was president of the local temperance union; her killing made the front page of the New York Times. The next day her funeral made national news due to the eerie presence of a small army from the Ku Klux Klan, its members, donned in full regalia, drawn from three surrounding states. It was September 1925, and Al Capone had just taken over the Chicago Outfit, evangelist Billy Sunday was converting thousands to temperance, and the KKK had marched on Washington, DC. During its first half century of statehood, Iowa lurched from wet to dry and back eight times before Prohibition was ratified in 1919. And when Iowa was still a territory, its Black Codes imprinted generations with a legacy of intolerance and racism. Mrs. Cook and the Klan is a true crime investigation that not only sheds new light on Myrtle Underwood Cook's unsolved killing but also explores the confluence of the social, political, and economic forces that brought the Klan, street gangs, a local mob boss, and the temperance movement together in a small American town.