Edward Bulwer-Lytton's book is ostensibly a work of science fiction. It deals with an underground race of advanced beings, masters of vril energy - a strange power that can both heal and destroy - who intend to leave their subterranean existence and conquer the world. But the book has been seen by many as a barely concealed account of hidden wisdom, a theory that has attracted many strange bed-fellows, including the French author Louis Jacolliot, the Polish explorer Ferdinand Ossendowski, and Adolf Hitler.