In a city that never was, in an America that never was, on a snowy night at the end of winter, two detectives find a body on the roof of a skyscraper.

It's 1922, and Americans are drinking in speakeasies, dancing to jazz, stepping quickly to the tempo of modern times. Beside the Mississippi, the ancient city of Cahokia lives on - a teeming industrial metropolis, containing every race and creed.

Among them, peace holds. Just about. But that body on the roof is about to spark off a week that will spill the city's secrets, and bring it, against a soundtrack of wailing clarinets and gunfire, either to destruction or rebirth.