LESLIE KLINGER knows more about Sherlock Holmes than nearly any other living scholar. Among his two-dozen books about the fictional detective is the exhaustive "The New Annotated Sherlock Holmes", which offers notes on the four novels and 56 stories written about Holmes by Sir Arthur Conan Doyle. But when it comes to imagining new adventures for the London-based Holmes, Mr Klinger has run into trouble. At issue is a new compilation of Holmes-derived stories which Mr Klinger has edited with Laurie King, a mystery novelist. Conan Doyle's heirs claim that they have the right to extract license fees or suppress publication. Mr Klinger has responded by filing a lawsuit in a federal court in Chicago, arguing that he has not infringed copyright as the content in question is now in the public domain. The situation is muddled by differing copyright regimes in America and elsewhere. No one disputes that the copyright has expired on Conan Doyle's work anywhere where protection ceases 70 years after an author's death (he died in 1930). Yet when America reformed its copyright rules in 1978 to introduce a "life plus" model in harmony with the rest of the world for works created starting in 1978, it retained its older term-limited system for property created between 1923 and 1977. Works produced within that range have had their expiration extended to a fixed 95-year term from first publication; anything produced earlier is in the public domain. This umbrella of protection covers ten Holmes stories published in America for the first time as part of "The Case-Book of Sherlock Holmes" in 1927. These stories are still under copyright until January 1st 2023. Mr Klinger says in his lawsuit that the estate has demanded a licence for access to parts of Holmes's history, characterisation and chums. Back in 2010, when he and Ms King prepared another collection of Holmes-inspired stories called "A Study in Sherlock", he and his publisher, Random House, agreed to assuage the estate to avoid litigation, even though the fan fiction avoided any story elements that remain under copyright. The fee was $5,000, Mr Klinger has told the New York Times. But for a sequel called "In the Company of Sherlock Holmes", to be published by Pegasus Books, the editors intend to stand their ground. Mr Klinger says that in December 2012 the Conan Doyle estate threatened to alert retailers of the copyright dispute were the book to go ahead without license. He adds that Pegasus now refuses to publish the work without an affirmative declaration that no legal action will be lodged against it, nor will attempts be made to interfere with distribution.

The estate also asserts some trademark rights on the Holmes characters, but Mr Klinger confirms to your correspondent that this was not part of the license claim. Jennifer Jenkins, the director of Duke University's Centre for the Study of the Public Domain, says trademark protection would be inapplicable, in any case. "Trademark law doesn't fit what they're claiming to own or what they're trying to stop," she says. Ms Jenkins also dismisses any copyright claim the estate might have to any pre-1923 elements of Holmes's biography. "The problem is that Sherlock Holmes and Watson are quite clearly in the public domain." The estate did not respond to a request for details about its intellectual property.

To avoid similar disputes, high-profile film-makers, television producers and other creators have paid the estate in the past, including for the BBC's "Sherlock", CBS's "Elementary" and the Hollywood films starring Robert Downey junior (for which Mr Klinger served as a Holmes expert). But many other uses of Sherlockiana have sought no permission, and have received no sanction. This includes Ms King's own series of "Mary Russell" books, told from the perspective of Holmes's eponymous protégé, colleague and, finally, wife.

An expert in the duration of copyright terms in America, Peter Hirtle of Cornell University finds no basis for the Conan Doyle estate to claim general ownership over aspects of Holmes from stories that are in the public domain. "Let's imagine that the fact that Holmes plays the violin was included for the first time in one of the copyrighted stories," he says via e-mail, "then it can't be included in any new story that draws on the public domain versions." But if the "Company" stories rely entirely on public-domain elements, then the estate has no ground to stand on, he adds.

As a cautionary tale for the Conan Doyle estate, Mr Hirtle refers to the long-running dispute between Carol Loeb Shloss and the estate of James Joyce over her use of material relating to Joyce's daughter Lucia. In 2006 Ms Shloss filed for declarative relief to use the material under the scholarship provisions of fair-use doctrine. The Joyce estate contested the action and lost, and was forced in 2009 to pay $240,000 in legal costs. Sometimes, writes Mr Hirtle, "there is a cost to claiming rights where none exist."