Edward Bulwer-Lytton 
Vril [PDF ebook] 
The Power of the Coming Race

This early science fiction novel offers a fascinating vision of a shadowy underworld populated by strange and beautiful creatures who closely resemble the angels described in Christian lore. These beings, known as Vril-ya, live underground, but are planning soon to claim the surface of the earth as their own — destroying humankind in the process.