The Descent by Jeff Long
This nonsensical twaddle sees humanity learn an offshoot of humanity dwells in the abyssal world beneath the Earth. They have murderous intentions. This causes people to a horrible horrible life as they try to stop them. This is badly written, sexist and racist. How are they even breathing underground?
“Built religions against them.”
“Something's gone horribly wrong down there.”
“Before history ever began.”
“If you gaze for long into an abyss, the abyss gazes also into you.”
“Before you kneel, it would be wise to know to whom you kneel.”