At her death in 1997, Jean Conan Doyle bequeathed her father’s copyrights to the Royal National Institute of Blind People. The institute sold the rights back to the Doyle heirs, who transferred them into a family-owned company.

In recent years the estate has licensed the characters for mystery collections with Christmas themes (“Holmes for the Holidays”) and supernatural overtones (“Ghosts in Baker Street”). Mr. Lellenberg said a volume of vampire-theme Holmes stories was also being considered.

Image Jude Law as Dr. John Watson. Credit... Warner Brothers Pictures

“Vampires are all the rage these days,” he said. “There’s no end.”

As Holmes has endured, so have challenges over his ownership. In court cases that started in the late 1990s, Andrea Plunket, the ex-wife of Mr. Reynolds, the producer, filed suits against the Conan Doyle estate and other companies, saying they violated her rights to the characters. Her family had financed the purchase of the Conan Doyle properties from the Royal Bank of Scotland, and after she divorced her husband (and became the companion of the socialite Claus von Bülow), she said those rights were hers.

Federal courts have repeatedly ruled against Ms. Plunket, and her attempt to trademark the Sherlock Holmes name was denied. But in a telephone interview, she said she was the administrator of the Sir Arthur Conan Doyle Literary Estate, and that when Jean Conan Doyle’s advisers served Ms. Plunket’s family with a notice of copyright termination, they sent it to a non-existent address.

Ms. Plunket, who now operates a bed-and-breakfast in Livingston Manor, N.Y., said that Mr. Lellenberg and his colleagues were the aggressors. “He has one huge advantage,” she said, “which is the name Conan Doyle, which he brandishes, of course.”

Ms. Plunket said that she had a limited involvement in the making of Mr. Ritchie’s “Sherlock Holmes” film, and that she spoke frequently with its producers and visited its set. “Nobody asked me for my advice,” she said “They didn’t say, ‘Oh, well, Mrs. Plunket, tell us who you want to play Sherlock Holmes.’ I had no legal right.”