The Necronomicon.

I've often used book titles as prompts. But in the past, I stuck to a couple of basic rules: 1) It should be the title of a real book. 2) It should be a book which I have actually read.

I decided it was time to try something different: Start using, as prompts, the titles of books which were prominently mentioned in works of fiction, but the book itself does not exist in the real world. I began with one of the most famous of such books; one repeatedly mentioned in H. P. Lovecraft's horror stories. Usually known as the Necronomicon, although I believe Lovecraft established that this was actually the name applied to a Greek translation of an occult work originally written in Arabic and called by the title Al Azif. Just reading that book (in any language) could do lasting damage to your mental health -- and trying to use the occult secrets contained within its pages tended to lead you to a gruesome fate.