When Dr. Tom More (of Love in the Ruins) is released on parole from state prison, he returns to Feliciana, Louisiana, the parish where he was born and bred and where he practiced psychiatry before his arrest. Upon arriving, he notices something strange in almost everyone around him: unusual sexual behavior in women patients, a bizarre loss of inhibition, a lack of complexity in speech—even his own wife's extraordinary success at bridge tournaments, during which her mind seems to function like a computer.

With the ingenious help of his attractive cousin, Dr. Lucy Lipscomb, More begins to uncover a criminal experiment to "improve" people's behavior by drugging the local water supply. But beyond this scheme are activities so sinister that even Tom More wouldn't believe them if he hadn't witnessed them with his own eyes.