"The Drowning Pool" is an unusual film because it's a sequel to a film made nine years earlier. In 1966, Paul Newman starred in an excellent detective film, "Harper". Now here in 1975, Lew Harper is back and working for a family in Louisiana. Like Harper of old, this one is very bright but also far from perfect--and gets the crap kicked out of him periodically.
As far as the story goes, the plot is a bit complicated. It's also initially not super-interesting. Hold on...resist that urge to turn it off. This is because despite the many different directions the film goes, by the end of the film it all comes together and there are a lot of exciting moments. One of the best is the water scene-- a huge and impressive bit of camera-work that you just have to see to believe. Another is the ending and the many little surprises that occur.
The bottom line is that this is just a film you need to see to understand and appreciate. Well made and well worth seeing.