Something strange is happening to the city's water supply. It is up to Arnold and Gerald to find out what. When they descend to the depths of the sewer and discover the Sewer King, an even bigger mystery unfolds. Will Arnold and Gerald be able to save the city's water supply before it's too late?
This is a reasonably interesting sequel to a fairly decent episode of the TV show. The ongoing highlight is Arnold's compassion and determination to do the right thing driving the story at every stage.