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If the extent of your knowledge of Arthur Conan Doyle’s famed detective is the phrase, “No shit, Sherlock,” Guy Ritchie’s Sherlock Holmes is a delightful, if somewhat wayward, introduction. Played by Robert Downey Jr. with an Iron Man body and Wonder Boys wit, this new Holmes may be a bit too 19th-century Bond for fans of Conan Doyle. But this whiz-bang interpretation sure is fun.

At the beginning of the film, Holmes is a semi-crazed shut-in, holing up at Baker Street and doing drugs to quell the overactive brain that hasn’t had a case to work on in months. “You do know what you’ve been drinking is for eye surgery!” his exasperated friend and biographer, Dr. Watson (Jude Law), tells him. Watson nudges Holmes back out into the world one night to meet his fiancée, Mary (Kelly Reilly). “Wear a jacket,” Watson says. “You wear a jacket,” the detective retorts.

Soon enough, though, England needs Holmes again. A serial killer, Lord Blackwood (Ritchie regular Mark Strong), has been captured and put to death. But before he’s hanged, he warns the detective that not only will there continue to be murders, “You must accept that this is beyond your control.” Of course, this too makes Holmes twitchy. And when an old flame, criminal Irene Adler (Rachel McAdams), also comes to him with a related mystery involving a “ginger midget,” the game, to his childlike delight, is truly afoot.

It took a handful of screenwriters to concoct the film’s premise, with Blackwood going Voldemort as the case veers into the dark arts. There are literal smoke and mirrors, too, with resurrections and kills that seem supernatural—to the untalented eye, at least. Disguises, chemistry, and even a dip into mysticism bring Holmes closer to the truth, with interiors that are aptly dungeon-like. Outside, we see an industrial London, its vistas brown, gray, sweaty, and sooty, with seemingly fewer completed buildings than endless catwalks and construction.

Punctuated by explosions and fisticuffs (less than Ritchie’s usual, yet still faithful to the character’s hobby as a bare-knuckled boxer) and accompanied by inspired repartee (his banter with Eddie Marsan’s Scotland Yard inspector is particularly entertaining), this two-plus-hour treatment moves as quickly as Holmes’ mind. McAdams is feisty and Law a suitable straight man, but it’s Downey’s performance that charms. His Holmes is a smarty-pants scalawag, the kind of character that, admittedly, has proved the actor’s forte throughout his career. But it works in throwback England as well as it does in present-day, hero-thirsty America—and it looks as if he’s got another franchise on his hands.