Charles L. Grant was an important figure in the horror fiction boom of the 1980s; this 1978 novel set in the fictional town of Oxrun Station, Conn., helped make him one of the more prominent of the new horror authors of the time.
Grant was a practitioner of what he called "quiet horror," and this tale of cultists and sinister missing library books fits that description. I'm having a hard time imagining the Courant's book critic writing anything with an exclamation point, but that's what review blurb punctuation does.