The title Plutonia refers to the novel's setting in a lost land. It is an underground world having its own sun, called Pluto for the Roman god of the underworld. The terrain is marked by dramatic geographic features and inhabited by monstrous animals and primitive people. These are essentially the animal and plant life of previous geological periods in their natural surroundings. As the five scientists venture deeper into the underground area, they encounter many adventures, more and more ancient life forms, back to dinosaurs and other Jurassic species.