Throughout, 33 full-page illustrations by Gahan Wilson (one per chapter, plus one on the inside back cover) punctuate a tale heavily influenced by H. P. Lovecraft.

The title is a line from Edgar Allan Poe's "Ulalume" and Zelazny thanks him as well as others – Mary Shelley, Bram Stoker, Sir Arthur Conan Doyle, Robert Bloch and Albert Payson Terhune – whose most famous characters appear in the book.

Though never explicitly stated, various contextual clues within the story (the most obvious of which is the appearance of Sherlock Holmes or "The Great Detective") imply that it takes place during the late Victorian period.

When these conditions are right, men and women with occult knowledge may gather at a specific ritual site to hold the doors closed, or to help fling them open.

In addition, there is a Witch ("Crazy Jill"), a Clergyman (Vicar Roberts), a Druid ("Owen"), Victor Frankenstein ("The Good Doctor"), Sherlock Holmes ("The Great Detective"), a "Mad Monk" ("Rastov" – apparently modeled after Rasputin), and grave robbers or Hermetic occultists ("Morris and McCab" – based either on real-life grave robbers Burke and Hare[3] or a reference to a real hermetic of the time, MacGregor Mathers).