Should you require an antidote to the bloat and lethargy of Christmas, you could do a lot worse than check out A Game of Shadows, a rousing bit of slash-fiction, which at times feels more indebted to Flashman or James Bond than to the writings of Sir Arthur Conan Doyle. Chasing the trail of 2009's Sherlock Holmes, director Guy Ritchie isolates a subtext and then runs with it. His Holmes is not the cerebral, largely sedentary sleuth who holds court from the comfort of a Baker Street armchair. Instead, he gives us Holmes as seductive best mate; as martial arts adventurer; as the can-do hero of a tale that is colourful and boisterous, with barely an ounce of fat on its bones.

The tone is set in the opening minutes as a bomb goes off in Strasbourg and Holmes (Robert Downey Jr) finds himself single-handedly repelling a band of hired goons. From here it's full steam to the finish line, via anarchist plots and exploding trains, as a chain of action set-pieces stand in for the plot. One minute our hero is ensuring that Watson (Jude Law) arrives at the church in time for his wedding. The next he's pitched into battle with the dastardly Moriarty (Jared Harris), who has hatched a scheme to foment a war in Europe and then trade arms to the highest bidder.

"My horror at your crimes is matched only by my admiration at the skill it took to achieve them," purrs Holmes, who recognises a worthy adversary when he sees one. Certainly Downey Jr's louche acting style finds a neat balance with Harris, who plays Moriarty as a puckish, dapper Satan, his ratty teeth glinting behind fox-red facial hair. Holmes and Moriarty are on collision course, rattling at speed towards a final lovers' embrace atop the precipice. And for once, not even the hyperventilating Watson can come between them.

In the meantime, I'm tempted to credit Holmes with rescuing the director from his own, personal Reichenbach Falls. Not long ago, Ritchie looked dead in the water; dashed by the hell of Swept Away and sunk by Revolver.

Yet now, with these rollicking Victorian capers, the director looks to have finally found a franchise to justify his Bullingdon-boy aesthetic.

A Game of Shadows stands as a valentine to the public-school buccaneer. It provides Ritchie with a licence to run wild with Gypsies, trade punches with cossacks, or just generally arse about in expensive hotels. It gives us anarchy as panto and global espionage in the guise of a homoerotic stag weekend.

"Tell me Watson," pants Holmes, "are you as happy at this moment as you would be on your honeymoon in Brighton?" But the question is merely rhetorical. A Game of Shadows assures us that escapism is good, that mischief must be celebrated. Holmes and Watson are happy and their escapades play out with such grace and brio that the fun is infectious.