The estate of Arthur Conan Doyle has filed a lawsuit alleging that an upcoming Netflix film about Sherlock Holmes' younger sister infringes on the Holmes stories that remain under copyright.

The estate claims that `Enola Holmes,` starring Millie Bobby Brown, depicts the legendary detective as warm and friendly, a characterization that only appears in the final 10 Holmes stories. The estate has zealously sought to protect its rights to Sherlock Holmes, even as most of the stories have slipped past the 95-year window for copyright protection in the U.S.

In June 2014, the 7th Circuit Court of Appeals affirmed that the character is in the public domain, and rejected the estate's effort to block distribution of a book of stories based on the Holmes mysteries. Conan Doyle wrote 56 stories and four novels based on the character between 1887 and 1927. All of them will be outside of U.S. copyright protection in 2023.

The Netflix film is due out in August, and is adapted from `The Enola Holmes Mysteries,` a series of six novels written by Nancy Springer, and published between 2006 and 2010.

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Netflix is being sued over the upcoming release of Millie Bobby Brown's 'Enola Holmes,' a film about Sherlock Holmes' exceptional sister. Read more about the lawsuit, at the link in bio. (📷: @gettyentertainment)

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In the lawsuit, the estate alleges that Springer's novels draw on the 10 stories published between 1923 and 1927, in which the coldly analytical detective is depicted - for the first time - as capable of empathy and friendship. The suit quotes from a scene in one of the novels in which Sherlock Holmes express `controlled anguish` when Dr. Watson goes missing, and is presumed dead or kidnapped.