Dr. John Pearly is an affable, turn-of-the-century con man who sells a patent medicine whose primary ingredient is whiskey. He resurrects a broken down steamboat with a makeshift crew and challenges the respectable but arrogant Captain Eli to a winner-take-all river race. Pearly hopes his nephew Duke will serve as pilot, but the young man stands accused of murdering a 'swamp rat' who threatened the honor of 'swamp girl' Fleety Belle. After Duke is arrested, Pearly tries to raise money for a lawyer by charging admission to a wax museum aboard his ship. Ultimately he gambles it all in the river race to Baton Rouge, where he hopes to find a witness whose testimony will free Duke.