Arthur Conan Doyle probably wouldn’t like what the new "Sherlock Holmes" does to his iconic character. Don’t worry about him. He’s dead.

Director Guy Ritchie ("Snatch," "Lock, Stock and Two Smoking Barrels") reinvents the famous detective as a quippy action hero. He still rocks the deductive reasoning and keen observation skills, but now he can do both while throwing punches in slow-motion.

It’s a bold update, and it only really works for one reason: Robert Downey Jr.

In another engrossing performance, Downey brings his cocky "Iron Man" attitude to 1890s London. Think Tony Stark with a hint of Adrian Monk, add a delightfully thick British accent, and Downey  is the swaggering Sherlock Holmes for the X-Box generation.

Downey’s performance is made even better by Jude Law, playing Dr. Watson as the long-suffering but supportive "spouse" to the eccentric crime solver. Both men have female love interests, but they aren’t half as entertaining as the bond between longtime partners. When an investigation leads to fisticuffs, the men almost instinctively know who will fare better against each respective henchman.

Plot hardly matters. The mystery involves the mysterious reappearance of Lord Blackwood (Mark Strong), a magic-wielding goon who is seemingly hanged in the film’s opening act. It’s engaging enough, but you won’t need to be a super-sleuth to figure it all out.

Rachel McAdams appears as Irene Adler, a former flame of Holmes who is somehow involved with the bad guys. She’s on the good side, probably, but her only function in this movie is to set up the inevitable sequel.

Ritchie directs with his usual slam-bang style, and even with a running length over two hours, "Sherlock Holmes" breezes along on the spark between Downey and Law.

It won’t win over any English professors, but with so many other Sherlock Holmes movies to choose from, they can probably tolerate a few slow-motion punches without crying blasphemy.

Grade: B+