MONTIGNY-LE-BRETONNEUX, France – This is the story of how a 1916 silent film starring William Gillette, the most renowned Sherlock Holmes interpreter of his day, came to be lost for nearly a century. And then, miraculously, found.

But we'll get to that.

In the meantime, if anyone ever writes a mystery about a detective searching for a long-lost artifact, in the shadowy corridors of a film archive so atmospheric it could have been designed for the movies, then there is only possible archive for the job. Call off the location scouts. We have a winner.

The archives of the Cinémathèque Française are housed in a sprawling 19th-century military compound crouching against a hillside, situated among trees, chirping birds and a panorama of greenery. Fort de Saint-Cyr was built in response to the 1870 Prussian invasion of France, 16 years before Sir Arthur Conan Doyle introduced his sleuth revered around the world.

One day in February 2014, a staff member of the Cinémathèque archive, 15 miles southwest of Paris, sat down to catalog another day's worth of fragile nitrate films. Alphabetically this was an "S" day. Archivist Emmanuelle Berthault cracked open the first of several moldering film cans shipped over from the nearby Centre National du Cinema.

"Most of the films," she later wrote to a fellow film historian, "are pretty well identified and we know what we are going to discover in the cans. But one of the titles was mysterious, it was only under the title 'Sherlock Holmes.' "

The cans contained three different films: a German film produced by UFA in 1937, an episode of a 1954 TV series ("The Case of the Texas Cow Girl") and a "very puzzling" third, made up of five cans of reels of a duplicate negative, or "dupe neg" in archival parlance.

"It was very easy to identify the film," Berthault recalled. "There were flash-titles, with the title, the director's name, the production company and the name 'William Gillette.'

"But frankly I didn't realize, at this moment, the importance of the discovery."

No one knows how the "Sherlock Holmes" with the French-language intertitles, the version shown to the French public in 1920 four years after the U.S. premiere, ended up at the Cinémathèque. But there it was, on a table at the Cinémathèque archive.

"It was fantastic," said Celine Ruivo, director of the Cinémathèque film collection. "We knew the importance of what we had. Nobody had it. It was in excellent condition, complete."

Go-to stage Sherlock

By the time Gillette starred in his first and only film, he was known throughout America and England as the go-to stage version Sherlock. Resembling a Victorian-era Gary Cooper, he toured far and wide as Holmes, popularizing the deerstalker cap, the curved pipe and the catchphrase "Elementary, my dear fellow," not found in any of the stories. "Elementary, my dear fellow" became "Elementary, my dear Watson" once sound pictures came in.

Gillette was 63 when he shot the movie at Essanay Studios in Chicago in the spring of 1916. Most of it was filmed inside, but there are a handful of exterior scenes — Holmes stepping out of a horse-drawn carriage in a cobblestone alley — in which Chicago passed for London.

Seen today, Gillette's screen charisma seems modern in its restraint.

"It breaks the stereotype we have of silent film acting being overly broad, overly gestured," said San Francisco Silent Film Society board president Robert Byrne, who has overseen the film's restoration in collaboration with the Cinémathèque Française.

"Film acting got pretty subtle pretty quickly," he said. "Nonetheless, this was Gillette's first and only screen appearance. And he figured it out right away. His is the first major Sherlock on film. And in its way this wasn't just a lost film; it was a lost play. The restoration brings Holmes' first appearance on the stage back to life."

Long restoration process

The process of restoring even a first-rate copy of an ancient film involves many steps and months. The Cinémathèque's Ruivo notified Byrne about the rediscovery of "Sherlock Holmes" in April last year. Ruivo then shipped the seven reels (roughly two hours' worth) to Italy's Cineteca di Bologna, one of the world's premier restoration facilities.

A restoration team made physical repairs to the footage and scanned the film digitally at high resolution. From there, Byrne was sent 114,000 separate, sequentially numbered computer files. Using sophisticated software, he undertook the job of removing dust and scratches and finessing instances of visible nitrate deterioration. Finally, Byrne and Ruivo went to Bologna to oversee the restoration of the color tint.

"The very first question [about the movie] should be: Is it any good?" Byrne said. "It's not a great film. But it's a good film." Visually, he said, "you get some pans, you get dollies, you get some interesting double exposure effects in some shots."

A May 1916 Chicago Daily Tribune review praised the movie as "a production to which Essanay may point with pride and may file away in the strong box for future and again future revival."

That future was a long time coming.