Gertrude Barrows Bennett has been called "the woman who invented dark fantasy". She wrote under the pseudonym Francis Stevens. "Citadel of Fear", republished and rediscovered as a "lost classic" in 1970 (then published as a book for the first time) was considered a masterpiece by fellow writer H. P. Lovecraft.

A pair of adventurers discover a lost city in the Mexican jungle. One of the adventurers succumbs to an evil god while the other one falls in love. Back in the US, the adventurer possessed by the evil god starts using his powers to mutate civilians. A reckoning between the two adventurers is inevitable...