Trot and Cap'n Bill are fishing in a rowboat, one fine day, on Lake Quad, the main body of water near the Emerald City. Suddenly a giant lake monster surfaces beside them. The creature, who calls himself Quaddle, explains that he was buried under the mud and rocks of a "lakequake" for "a zillion years." Another lakequake has now freed him into a new world, in which "flangosaurs and humpdoodles" no longer exist. Quaddle confesses that his thought processes are jumbled by his experiences; but a mysterious person has complained of troubles and asked him to find a "champion." And so he accosts girl and sailor: "Are you champions?"
As is typical of their relationship, Trot is eager to go and help the unknown sufferer; the Cap'n is somewhat more cautious, but not enough to prevent a new adventure. Quaddle transports the two humans (in his cheeks) under the lake, to a subterranean land, lit by phosphorescent fungi and populated by mushroom people. The Shrooms' city has been devastated by the lakequake, and their remnants are being oppressed by a dictator. The villain, a one-eyed Shroom named Rottug, has obtained a Magic Mind-Switcher from the Nome Kingdom; he captures the newly-arrived humans and switches minds with Cap'n Bill. With a more powerful physical form, Rottug can capture the Mutliplying Overcoat that is an object of veneration by the Shrooms; he uses it to duplicate Cap'n Bill's body into a small army of Cap'n Bills, all controlled by Rottug's mind, to secure his mastery of the Shroom domain.
The opposition — Trot, Cap'n Bill's mind in a Shroom body, and a nascent Shroom resistance — try to counter Rottug's coup. What follows is a dizzyingly complex tale involving duplication and giganticism, minds and souls in other bodies, Shroom politics, Shroom history, Shroom religion, an enormous merman, a mysterious and never-seen stone giant, and much more. In the end, Trot and company manipulate Rottug's uncontrolled ambition into a "pop" of self-destruction, so that proper order can be restored.
Ingersoll and Shanower created their fiction through an unusual method. Ingersoll wrote the first chapter, Shanower the second; they continued to alternate through the twelve chapters of the work, with no pre-conceived plan. The process lasted from 1982 to 1988. Shanower provided lush illustrations.
Some of the story's visual elements are striking, from the phantasmagoric ruin-strewn mushroom realm, to lightning-producing bees in a misty blue landscape. The story has marked resemblances with Shanower's other tale of subterranean mushroom people, "Dorothy and the Mushroom Queen."