In the spring of 1927 the Mississippi River valley region floods in what is perhaps the greatest natural disaster in the history of the United States. The flood and its aftermath will profoundly change government, society and race relations in the region.

The vast flood covers a huge amount of land in water up to thirty feet deep, displacing about one million people in a nation of 120 millions. Flooded areas are roughly equal in size to Massachusetts, Connecticut, New Hampshire and Vermont combined. Thousands die, and over a quarter of a million blacks live in refugee camps for several months. The Red Cross feeds nearly 700,000 refugees for weeks. Many people of all races leave the area permanently.

The flood ends the South's planter aristocracy, initiates a wave of black migration to the North and lays the foundation for what will ultimately become the Federal government's New Deal intervention in the region. The book covers several decades of regional development and politics prior to the flood, establishing the historical reasons for settlement patterns and investigating in detail the rationale behind the area's "levees-only" river containment policy.

The book initially focuses on several individuals important in early river development and illustrates how they, in concert with the times, influence the policies that will lead up to the disaster. The actual flooding is then considered, with particular attention focused on the levee failures. The aftermath is explained both in the immediate effects to the region as well as the larger national significance.