Sir Arthur Conan Doyle died in 1930. He wrote fifty-six Sherlock Holmes stories, all but ten of which were published prior to 1923, and are therefore in the public domain in the U.S.
Leslie Klinger is a Sherlock Holmes fan, and has decided to publish a book featuring Holmes and Watson. Doyle's estate thinks Klinger needs a license from them to do so. Klinger doesn't agree.
This case has already been heard by a U.S. District Court, and by the U.S. Court of Appeals for the Seventh Circuit, both of whom agreed that Klinger does not need a license if, as the Seventh Circuit found, he is only drawing on aspects of the characters from the public domain works. The Doyle estate argues that so long as the character of Holmes continues to be developed, the copyright clock essentially resets with every new publication. The courts that have heard the case so far haven't been sympathetic to this argument, probably in part because it would potentially extend the copyright protection for the Holmes character indefinitely.
Having lost in the lower courts, the Doyle estate has now asked the U.S. Supreme Court to issue a stay on the lower court ruling (essentially delaying publication of Klinger's work) until such time as the Supreme Court can consider the full case.
It is an interesting case, and it seems likely that the Supreme Court will simply let the lower court ruling stand. An indefinite copyright term for characters runs contrary to both the Copyright Act and the Constitutional grant of power to Congress to create a copyright system to protect authors for a "limited time." If the pre-1923 works are in the public domain, that has to mean something. The material set forth in those works should be freely available to anyone.