Speakeasy follows the investigation by Milwaukee patrolman Jud Minor into the killing of fellow officer Landis "Suthrin" Humphreys, whose bloody body is found inside the doorway of a Sixth Ward speakeasy just after midnight on Christmas Day, 1931. Thanks to front-page articles published in the Milwaukee Tribune and written by a less than scrupulous newspaperman who has his own agenda, Patrolman Minor quickly becomes a celebrity and is assigned by the police chief as "Acting Detective" on the case. Minor's investigation soon broadens beyond the Sixth Ward and eventually takes Jud into the heart of the Jim Crow South.

Quite apart from being a gripping and beautifully written crime drama, this work of historical fiction also provides a vivid snapshot of Prohibition-era Milwaukee and includes many actual persons from Milwaukee's past, not least of whom is its protagonist, Judson W. Minor, the first African-American officer on the Milwaukee police force. Among the other historical figures are Daniel Webster Hoan, Milwaukee's first Socialist mayor; J. Anthony Josie, co-founder of the Wisconsin Enterprise-Blade, who was widely known at the time as "The Mayor of Bronzeville" and, alternately, as "The First Mayor of Black Milwaukee"; Milwaukee Police Chief Jacob Laubenheimer; and Third Ward Mafia boss Joe "Piddu" Vallone. Other lesser-known historical figures are also prominent in the story.