Private detective Lew Harper (Paul Newman) investigates a blackmail plot in Louisiana bayou country involving the nymphomaniac daughter (Melanie Griffith) of an old flame of his, Iris Devereaux (Joanne Woodward). He is caught up in a power struggle between Iris and oil tycoon Kilbourne (Murray Hamilton). At one point, the complicated plot has Harper and Kilbourne's wife Mavis (Gail Strickland) locked in a hydrotherapy room, with the water rising to the ceiling, hence the film's title.
