A Harry Potter fan created a lexicon, available on the internet. The lexicon was popular with everyone, including J.K. Rowling and the people who made films about her books. Rowling wrote on her website "This is such a great site that I have been known to sneak into an internet cafe while out writing and check a fact rather than go into a bookshop and buy a copy of Harry Potter (which is embarrassing)." But when the fan published a book with the website's contents, Rowling sued, claiming copyright infringement. The defense was "fair use".
The court found that the defendant copied from the Harry Potter books, and indeed, copied too much and too clumsily to qualify for the fair use. The defendant failed to properly use quotation marks to indicate "borrowed" text. Also, the defendant borrowed too much expression from the originals. Significantly, Rowling had already prepared two lexicon-type works "Fantastic Beast & Where to Find Them" and "Quidditch Through the Ages", and the defendant had borrowed verbatim many of Rowling's own definitions relating to her Harry Potter fantasy world.
The court noted that there is a usefulness and a demand for reference guides to fictional worlds written by third parties, such as Paul F. Ford's Companion to Narnia: A Complete Guide to the Magical World of C.S. Lewis's The Chronicles of Narnia.
After closely weighing the "fair use" factors, the court issued a permanent injunction pursuant to Rule 65 of the Federal Rules of Civil Procedure against publication of defendant's book. The court found that where a prima facie showing of infringement was made, irreparable harm is presumed, but questioned whether that presumption had survived the U.S. Supreme Court's decision in eBay Inc. v. MercExchange LLC, 547 U.S. 388 (2006).
From the decision, it appears that the court was quite sympathetic to the defendant's apparent underlying goal of publishing a reference guide without Ms. Rowling's consent and was cognizant of the social utility of this type of publication. If the publisher had done a better packaging and editing job, had worked with the plaintiff to remove the more extensive borrowings, provide better citations and added a bit more "scholarly" commentary, it appears that the court would have found fair use.
As in most of these fair use cases, the devil is in the details.