"About a Boy" allows Hugh Grant to move his supporting character persona into the starring role.

The leading man Grant that Americans have accepted is the voice-stammering, eye-fluttering, hair-flopping romantic comedian of "Four Weddings and a Funeral" and "Notting Hill."

But when Grant gets a supporting role, he often plays a selfish sod with a hilariously acidic tongue, best illustrated in last year's "Bridget Joneses' Diary."

In "About a Boy" Grant plays Will, a selfish sod of a leading role. Will's worldview isn't withering, but he has made an art of avoiding human connections. "Everyone's life is like a TV show," he narrates. "I was the star of 'The Will Show,' and 'The Will Show' wasn't an ensemble drama."

Scripted by Peter Hedges as well as the brotherly duo of co-directors Chris and Paul Weitz of "American Pie" fame, "About a Boy" is based on a novel by Nick Hornby, who also wrote "High Fidelity" and seems to specialize in emotionally stunted men in their 30s.

Will is 38 and has never worked. He lives off the royalties of a cheesy Christmas carol called "Santa's Super Sleigh" that his father wrote in 1958. His flat is a Maxim reader's dream, appointed with the finest audio and video equipment in Bang and Olufson's and Sony's catalogues. He laments staying over at a girlfriend's place if she has no DVD player.

Early on Will enjoys a guilt-free relationship with a single mother - he is delighted when she breaks it off with him. Eager to duplicate the experience, Will joins a single parent's support group pretending to have a 2-year-old son.

Will's plan doesn't work, though. Instead of landing a new girlfriend, Will winds up playing unofficial Big Brother to Marcus (Nicholas Hoult), a 12-year-old outcast whose mother, Fiona (Toni Collette), is emotionally troubled.

I won't explain how the bond between Will and Marcus forms because a description would not do justice to how funny and naturally it plays on screen. The film jumps between Will's and Marcus' points of view, with each character allowed to narrate his own segments. Will's words are filled with forced detachment, while Marcus' roil with preadolescent confusion.

"About a Boy" defies categorization. From the outside it looks like a romantic comedy, but only a slim fraction deals with Will's love life. It also bears a surface resemblance to "Rushmore" with its relationship between a man who refuses to grow up and a boy who has grown up too quickly. But "About a Boy" is a purer comedy, not lacking in honest emotion but not as complex, either.

"About a Boy" defies other expectations, given its unlikely production team. The Weitz Brothers are best known for bringing strange warmth to gross-out comedy, a genre so home-grown it's no wonder their big hit is called "American Pie." After the Weitzes failed with the Chris Rock feature "Down to Earth," how could anyone expect them to succeed with a sophisticated and defiantly English style of comedy?

They do succeed, though, mostly because they are smart enough to let Grant be Grant and Hornby be Hornby. As in "High Fidelity," the script brims with pungent, quotable dialogue.

Though an excellent dramatic actor, Grant has become famous in comedies because no actor today plays humor with greater grace or ease. Here Grant works without his most familiar mannerisms. He does not stammer, he does not blink and the floppy hair has been reduced to a closely cropped tangle (though we learn later Will spends two hours at a salon having it "carefully disheveled").

Twelve-year-old Hoult is funny as Marcus without the forced punch lines Hollywood would have given him. Marcus hurts deeply and Hoult, whose eyebrows are sharply upswept like a Vulcan's, uses the pain to sharpen his character's deadpan humor.

Collette ("The Sixth Sense") often appears sullen and without makeup, a brave move in an industry where even the most serious actresses fear looking less than glamorous. Rachel Weisz ("The Mummy") appears briefly in a piddling role as one of Will's potential girlfriends.

"About a Boy" is funny in a way films avoid anymore. It seldom goes for the easy laugh, and often ends a scene unpredictably. It is fresh at a time Hollywood embrace staleness, especially in comedy.