Fans of Sir Arthur Conan Doyle’s Sherlock Holmes tales will recognize the sleuth they know in Nancy Springer’s 2006 YA mystery, The Case of the Missing Marquess. The Kirkus-starred novel centers on Sherlock’s much younger sister, Enola, who runs off to London to search for their mother, Eudoria, who’s gone missing; along the way, she meets another teenager—the Viscount Tewkesbury, Marquess of Basilwether—who’s being pursued by kidnappers. Enola’s other sibling, Mycroft, has become her guardian in their mother’s absence, and he’s determined to send her to a stodgy boarding school—that is, if he and Sherlock can locate her.

Sherlock plays a rather small role in the story, as Enola, a brilliant sleuth in her own right, spends much of the novel trying to avoid him. When he does appear, he’s very much Doyle’s creation—a cold, dispassionate man who’s dismissive of women, considering them inferior to men. A different kind of Sherlock appears in the new Netflix film adaptation Enola Holmes, which premieres on Sept. 23.

The film’s Sherlock is much warmer and has great admiration for Enola’s intelligence. He improbably displays feminist sympathies, telling his sister, “Whatever society may claim, it can’t control you.” He’s played by The Witcher’s Henry Cavill, a rather muscular actor who bears little resemblance to Sidney Paget’s classic magazine illustrations of a rail-thin Holmes. Peaky Blinders’ Sam Claflin doesn’t look like Doyle’s “larger and stouter” Mycroft, either.

It seems churlish to complain about such changes, though, when Enola, who’s played by Stranger Things’ Millie Bobby Brown, doesn’t even exist in the original tales. She’s Springer’s own wonderful creation—a truly talented detective, but not supernaturally so, and not so consumed with solving riddles that she ignores her own emotions. She’s also very funny, which comes across in Brown’s appealing performance; at one point, at an impasse, she even asks viewers, “Do you have any ideas?” (It bears mentioning that the film was directed by Henry Bradbeer, who helmed nearly every episode of Phoebe Waller-Bridge’s similarly fourth-wall-breaking Fleabag.)

Screenwriter Jack Thorne introduces other changes to Springer’s text. For instance, Enola is 16 years old, not 14, and there’s some mild romantic tension between her and the titular marquess (played by the Leonardo DiCaprio–esque Louis Partridge) that’s absent from the novel. The mystery surrounding the young noble is deepened, as well, which makes for a more engaging story; it involves a Parliament vote (apparently for the Third Reform Act) that necessitated moving the story from 1888 to 1884. (This makes the film a prequel to Doyle’s tales, which started with 1887’s A Study in Scarlet.)

In the film, Enola briefly attends the aforementioned boarding school, which, in the book, is never more than a threat; it’s run by the deeply unpleasant Miss Harrison, played to perfection by Fiona Shaw, who was recently nominated for her work on the BBC America show Killing Eve. The movie also adds Chewing Gum’s Susie Wokoma in the role of Edith, a skilled instructor of hand-to-hand combat whose appearances are brief but dazzling. The same can be said for Helen Bonham Carter, as Eudoria, who makes the most of her surprisingly limited appearances.

It’s Brown, though, who is the rightful star, with a performance that highlights not only Enola’s intelligence and independence, but also her heroism. In one moving scene, for example, she tells viewers why she has to help her friend out of a dangerous situation: “There are those that want to hurt him, and he has not the strength to stop them. And I do have that strength.” Such words will make any Sherlockian quibbles melt away.

David Rapp is the senior Indie editor.