“You are a work in progress,” Sherlock Holmes is told late in “Young Sherlock,” Prime Video’s new origin series about the world’s greatest detective. And it’s true: He’s young, irreverent, self-assured to the point of arrogance. (Though, to be fair, he’d be those latter descriptors no matter the age.)

“Young Sherlock,” though, is anything but a work in progress. Directed by Guy Ritchie, the eight-part series premiering Wednesday is, like its namesake, simply brilliant, a fusion of witty banter, clever humor and punchy action that keeps you on the edge of your horse-drawn carriage seat from start to finish.

Adapted from Andrew Lane’s “Young Sherlock Holmes” book series, which itself is based on the works of Arthur Conan Doyle, “Young Sherlock” opens with a mystery — quickly followed by a prison yard fistfight featuring none other than one 19-year-old Sherlock (Hero Fiennes Tiffin). That blend of cerebral and physical, a repeating motif in “Young Sherlock,” is standard operating procedure for the hit-or-miss Ritchie, who also directed 2009’s fantastic “Sherlock Holmes” and 2011’s slightly overstuffed “Sherlock Holmes: A Game of Shadows.”

But he doesn’t miss here. In fact, “Young Sherlock” is his best work in years. The series oozes with his signature style, from its blistering pacing and well-choreographed action sequences to its whip-smart humor and high regard for competence. (It wouldn’t hurt to brush up on your Shakespeare and Machiavelli and Sun Tzu.) But more than anything, it’s just unadulterated fun. There are mysteries to solve, secret locations (and passageways!) to discover, random stuff to blow up or set on fire — and it’s all infused with infectious charm and heart.

But back to those mysteries, the core of any good Holmes story — and what a good one we have here. Set in 1870s Victorian England, there are the murders of Oxford professors. And a Chinese princess with secrets aplenty and a talent for close-quarters combat. And a mother distraught with grief sent away to an asylum, who says “they” are listening to her every word. How do these all intersect — and, more important, how does it all involve Sherlock?

As the episodes progress, Ritchie and showrunner Matthew Parkhill weave a tale of intrigue that delights in surprising you. A perfect example: the portrayal of James Moriarty. A criminal mastermind long described as Holmes’ archenemy, in “Young Sherlock,” James is just an Oxford student — until his path crosses Sherlock’s and the two become close friends. Played by a show-stealing Dónal Finn, James at first comes across as a more charming version of Sherlock. But he’s so much more than he seems, and the interplay between him and Sherlock — centered on morality, ethics and whether the ends justify the means — is the highlight of the show. That Fiennes Tiffin and Finn share a crackling chemistry is just the cherry on top.

And Finn isn’t the only well-cast actor. Zine Tseng gives a chameleonlike performance as Princess Gulun Shou’an, while Natascha McElhone will break your heart as Cordelia, Sherlock’s mother. Max Irons is pitch-perfect as Sherlock’s older brother Mycroft (their constant needling of each other always ending with “brother dear” is an absolute delight), and Colin Firth is clearly having a blast as the loathsome Bucephalus Hodge, one of Britain’s richest men. (And each and every one of these characters is dressed to the nines, rocking color-coordinated three-piece suits and stunning dresses, thanks to costume designer Jany Temime.)

All of that is set to a punk- and rock-heavy soundtrack (Flogging Molly’s “Devil’s Dance Floor” may be the best needle drop for a British fistfight ever) and Ritchie’s typical cinematic flair. Expect plenty of stylish transitions and flourishes throughout, including my favorite: the visual representation of Sherlock’s mental calculations.

Early in “Young Sherlock,” there’s a toast to Sherlock and his “extraordinary future.” How prescient that would become. On its own, this series is a fantastic must-watch, but what a shame it would be if it didn’t get more seasons (which the final episode sets up). With “Young Sherlock,” the game is afoot, and here’s hoping it continues to be.

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'YOUNG SHERLOCK'

How to watch: On Prime Video March 4

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