The film is afoot!

Netflix released a new teaser for Enola Holmes—an upcoming movie based on Nancy Springer’s YA historical mystery series—on Twitter. The film, starring Stranger Things’ Millie Bobby Brown as Sherlock Holmes’ sister, is set to premiere on the streaming service on Sept. 23.

The tweet also includes a scrambled-word puzzle, albeit a fairly simple one; the tweet’s comments will quickly reveal the answer to those who are interested. (Netflix describes its @NXonNetflix account as its “home for all things geek”—a characterization that may or may not appeal to dedicated Sherlockians.)

Set in England in 1884, Enola Holmes seems to be largely based on Springer’s first series installment, 2006’s The Case of the Missing Marquess, which received a Kirkus Star. According to Netflix’s summary, the film follows the titular teen as she escapes her brothers—Sherlock (The Witcher’s Henry Cavill) and Mycroft (Sam Claflin, who played Finnick Odair in three Hunger Games films)—to search for their mother (Helena Bonham Carter), who’s mysteriously gone missing. Enola soon becomes “entangled in a mystery surrounding a young runaway Lord” and “unravels a conspiracy that threatens to set back the course of history.”

The teaser offers precious little detail about the film itself, but it does feature glimpses of several cast members, including the estimable Fiona Shaw, who was recently nominated for an Emmy for her role in the BBC America series Killing Eve, which is based on a series of spy novels by Luke Jennings. It’s unclear, as yet, what her role will be in the new film; rest assured, however, that the mystery will be solved shortly.

David Rapp is the senior Indie editor.