Merritt's work is notable for blending multiple genres before they were strictly defined:

: Beneath the ruins lies a subterranean world called Muria, filled with advanced technology, such as anti-gravity vehicles and "atomic" power.

: Opposing the Dweller are three ancient, angelic creators who have been "purged of dross" and seek to destroy their creation, though they are hindered by their lingering love for it. Literary Significance

: The central threat is the Shining One (or the Dweller), a beautiful yet malevolent entity made of light that lures people into a hypnotic, unholy stasis to feed upon them.