The suit notes that while most of Arthur Conan Doyle’s Sherlock Holmes stories, starting with the 1887 novel A Study in Scarlet, rest in the public domain, that is not the case with the author’s final 10 Sherlock stories, which were published 1923 and 1927.
The author’s estate filed a 19-page complaint against Enola Holmes in New Mexico federal court which claims (via Deadline) that the “copyright infringement arises from defendants unauthorized copying of original creative expression by [Conan Doyle] in copyrighted Sherlock Holmes stories.”