 Jim is increasingly puzzled by a series of strange events that seem to happen around his friend Giles "Gill" Peach who, like his father and forefathers before him, has gills.The boys are fascinated by pulp science fiction, and Gill begins building a device inspired by the "subterranean prospector" described in Edgar Rice Burroughs' novel "At the Earth's Core".Jim's father William, who periodically escapes the psychiatric facility run by Hilario Frosticos, is convinced that Gill is being manipulated by unscrupulous adventurers allied with Frosticos