This novel centres on a young, independently wealthy traveller (the narrator), who accidentally finds his way into a subterranean world occupied by beings who seem to resemble angels and call themselves Vril-ya. The hero soon discovers that the Vril-ya are descendants of an antediluvian civilisation who live in networks of subterranean caverns linked by tunnels. It is a technologically supported Utopia, chief among their tools being the "all-permeating fluid" called "Vril", a latent source of energy which its spiritually elevated hosts are able to master through training of their will, to a degree which depends upon their hereditary constitution, giving them access to an extraordinary force that can be controlled at will. The powers of the will include the ability to heal, change, and destroy beings and things; the destructive powers in particular are awesomely powerful, allowing a few young Vril-ya children to wipe out entire cities if necessary. It is also suggested that the Vril-ya are fully telepathic.