The time is 1951. A smooth-talking Chicago lawyer comes to chat with Sam Vincent, the former prosecutor of Polk County, Arkansas, about a dangerous subject--a big prison for violent black convicts near Thebes, Mississippi, up the Yaxahatchee River from Pasagoula. Thebes seems to have dropped out of the Union--letters and phone calls go unanswered, and the lawyer has questions that need answers. Would Sam--an ex-lawman, a white man and a Southerner--agree to go up there and find out what he can?

The ex-prosecutor takes on the job, but first he goes to see his old friend Earl Swagger, and tells him that if he isn't back in a week, Earl is to come looking for him. When Sam vanishes into the mists and swamps around Thebes, Mississippi, Earl packs his gun, explains to a distraught Junie that duty is duty and a promise is a promise, and sets off for Thebes, Mississippi to track his friend down.

Soon enough, Earl--who approaches Thebes and its sinister prison with the stealth of a good Marine on a recon mission--realizes that something very strange indeed is going on there, that the prison is more than just a place that chills the blood of even the most hardened convict, that in fact the whole town of Thebes is hiding a secret--and it's a place where people disappear all too easily, particularly inquisitive strangers, for whom burial in the swamps follows torture.