Matthew Broderick seems like a nice enough guy, quiet and self-effacing. Beneath the sweet exterior lurks a demoniacal comic imp. When he goes onstage, you’d better beware – particularly if you’re onstage with him.

In Larry Shue’s farce “The Foreigner,” he plays Charlie, a meek and socially awkward Brit; the structural support afforded by a corduroy-looking suit is the only thing keeping him upright. His friend, the brash soldier Froggy, leaves him in a Georgia lodge for three days of relaxation. To ease Charlie’s mind, Froggy tells the Americans that he can’t speak English. He’s “a foreigner.” Before long people are spilling their guts, unaware he understands every syllable.

Comic opportunities abound, and Mr. Broderick makes the most of them. Some of these were Shue’s invention, as when the dimwitted, Southern-drawling Ellard volunteers to teach Charlie proper English. A fork, Mr. Broderick dutifully repeats, is a “fow-werk,” a window is a “winder.” What really makes this fly is the sense, accurate or not, that Mr. Broderick and his co-stars are following their every comic impulse, making it up as they go.

The Roundabout’s hilarious production, which opened last night at the Laura Pels Theatre, treats “The Foreigner” as something like vaudeville, and amen for that. If the cast worked out all the comic business before walking onstage, they fooled me. More than once it looked like actors were straining with every nerve not to break character and laugh.

Some people in the theater world revile this behavior. It’s unprofessional, they say. Not to put too fine a point on it, but anyone who thinks this way is a cold, joyless curmudgeon who should go back to watching television. For one thing, Shue marked in the script various spots where an actor could experiment with lines from night to night. For another, we are in the hands of some of the sharpest actors in New York, and if one of them does something so funny it makes a castmate visibly stifle a laugh, so much the better for everybody.

As it did with “Assassins” last summer, the Roundabout has assembled an astonishing cast, something like an all-star lineup. Frances Sternhagen plays Betty, the lodge’s cheery proprietress. Mostly she plays the straight man here as the absurdity swirls around her, and she does it so sweetly you don’t notice that her smile masks the comic timing of a cold-blooded killer.

Is there anything Byron Jennings can’t do? Having just played Laura Linney’s sullen archaeologist husband in “Sight Unseen” and a rebel leader in “Henry IV,” he turns up here in a green beret and jaunty handlebar mustache. He makes Froggy’s comic bombast all the funnier by revealing its opposite. At one point, Charlie underscores a point by quoting Shakespeare: “Love is not love, Froggy, which alters when it alteration finds.” Froggy is charmed by this, until Charlie informs him that Shakespeare didn’t include his name in the original sonnet. “No. No, ‘e wouldn’t, of course,” says Mr. Jennings, making a priceless, abashed turn away from the audience.

Catherine and Ellard Simms, the siblings who are thinking of buying the lodge, are played by Mary Catherine Garrison and Kevin Cahoon. That would be the funniest gene pool in town. The able Ms. Garrison has a high voice, comic chops, and a dark streak; whenever she finds material ideally suited to her, the results may be tremendous. The inspired Mr. Cahoon is lanky and dangerous, at least on the night I saw the show. As Ms. Sternhagen was collecting breakfast orders, and Mr. Broderick and Ms. Garrison were looking on, Mr. Cahoon decided to start gnawing on the edge of the table. Why was he gnawing on the edge of the table? Who can say? Our loud, puzzled laughter nearly stopped the show.

Catherine’s fiance, the sinister David, is played by Neal Huff. He last turned up as Kippy, the cerebral shortstop/narrator of “Take Me Out.” I’m not convinced that Mr. Huff is a natural-born comic like Ms. Garrison. But he’s a first-rate actor, and the performance comes off superbly. He plays well with others.

At the risk of sounding naive, there’s a happy reminder in Mr. Huff’s performance, and in his castmates’: Very good actors make each other better. Their interplay can be its own reward. Director Scott Schwartz deserves credit for giving them enough room to play. The production could, to be sure, resound a little more deeply than it does. A few scenes don’t quite come off, like the exposition, which he seems to have punted. And he hasn’t helped Lee Tergesen find the right scale for the nefarious redneck. But as long as Mr. Broderick holds the stage, the production flies. It’s the fastest 165 minutes in New York.

Emboldened by pretending to be someone else, Charlie starts acting like Harpo Marx and sounding like Triumph the Insult Comic Dog. (At least when he answers in the affirmative, saying “Yais.”) Mr. Broderick knows it’s a mistake to emphasize Charlie’s spinelessness. Instead of fretting and flopping all over the stage, he focuses on Charlie wanting to preserve his dignity. Even when Ellard coaxes him into a ridiculous posture – juice glass on his head, banging it with knife, doing a kind of horrible kung-fu chicken dance in bathrobe and slippers – Mr. Broderick maintains a look of intense concentration.

To watch Mr. Broderick here is to suspect that all those months spent in “The Producers” trading ad-libs with Nathan Lane have created a lightning-fast comic monster. He seems poised to say or do just about anything, anytime. When I saw the show, while Charlie was teaching the Americans his language, Ms. Garrison tried to stifle a laugh. She gave herself a coughing fit. “Want tea?” Mr. Broderick finally asked in his small, Andy-Kaufman voice. Before she could answer, he was halfway across the stage. He poured her a glass and carried it back. Everybody, onstage and off, was laughing at this point, and I feared that Mr. Antoon, seated directly in front of Ms. Garrison, might soon be wearing her tea. But she drank it down, and everybody got composed, and Mr. Broderick returned to Shue’s script. “On with the lesson,” he chirped, with a little hop and a skip.

Until January 16 (111 W. 46 Street, between Sixth and Seventh Avenues, 212-719-1300).