Where the Evil Dwells — Clifford D. Simak

FOUR AGAINST HORROR
Secretly and in stealth, four puny humans set out to invade the heartland of Evil--the so-called Empty Lands, filled with every evil creature from the darkest of mankind's myths.

Harcourt went reluctantly to rescue his long-lost and almost forgotten fiancée. The Knurly Man, who was somewhat other than quite human, went to find the death that would be kinder than the future he foresaw. The abbot sought to recapture a fabulous prism in which the soul of a saint had been trapped. And the girl Yolanda was seeking the answer to a mystery and a question she did not know.

But already their coming and their purpose was known. The denizens of the Empty Lands were girding for war.

And behind all the Evil lay the most ancient of dark Powers, waiting patiently for the humans whose souls should set it free.