Early in Miss Pettigrew Lives for a Day, the title heroine played by Frances McDormand, a down-on-her luck "governess of last resort" who keeps getting dismissed by huffy high-class London employers, strolls the streets, dejected and down. On the soundtrack? A jazzy, swinging version of the Depression-era song "Brother, Can You Spare a Dime?" And that sweet-sour mix of bright horns and sad sentiments, swinging tempos and bleak prospects, in many ways sets the tone for the film. Adapting Winifred Watson's 1939 novel, Miss Pettigrew Lives for a Day is a nearly perfect piece of entertainment for grownups, as Miss Pettigrew's desperation inspires her to fake, fib and flail her way into a job as the social secretary to American actress/singer Delysia Lafosse (Amy Adams), a young woman in severe need of professional assistance and adult supervision. It's fairly easy to predict the rough curves of Miss Pettigrew's plot within moments of meeting the leads -- Miss Pettigrew will gain joy and confidence from her exposure to Ms. Lafosse, while Ms. Lafosse will acquire wisdom and character from Miss Pettigrew's example -- but the delights of this film are in the details, and everyone involved shapes this seemingly-featherweight entertainment with expert, steady hands.

Miss Pettigrew is not, in fact, a social secretary; however, she's prepared to do whatever is required. And so, in her way, is Delysia; the luxurious flat where she receives Miss Pettigrew is, it turns out, not hers. Delysia is staying there as the lover of nightclub owner Nick (Mark Strong), which makes it all the more necessary that Miss Pettigrew help get Delysia's overnight guest Phil (Tom Payne) -- son of the producer of a show Delysia hopes to land the lead in -- out the door as swiftly as possible before Nick returns. Miss Pettigrew is mortified, but hardly paralyzed, and she swiftly takes charge of matters. And, in the tradition of British farce, as soon as that crisis is averted, another is ready to take its place. ...

Directed by Bharat Nalluri and adapted for the screen by Simon Beaufoy (The Full Monty) and Simon Magee (Finding Neverland), Miss Pettigrew Lives for a Day might, at first, seem to hew close to the tone and tenor of well-established master-servant comedies of P.G. Wodehouse, where a flighty, frivolous upper-class protagonist's problems are put right by a steadfast, stalwart domestic; Bertie Wooster and Jeeves, for example. And, in fact, at first Miss Pettigrew seems to have Jeeves' deadpan, and Ms. Lafosse has the scattered thoughts and snug nightgowns of a Wodehouse heroine. But in Miss Pettigrew Lives for a Day, Beaufoy and Magee do something much more interesting, and much more inspired: Both our leads are in trouble, and both of them are frantic to escape circumstance. Delysia isn't just juggling Nick and Phil, but also dealing with Michael (Lee Pace), her piano player, whose recent thwarted proposal to her resulted in a champagne-fueled " ... altercation with the Yeoman of the Guard ..." and 30 days in jail. Miss Pettigrew is not only operating on borrowed credentials at a job that shouldn't be hers, but it turns out that she also witnessed up-and-coming fashionista Edythe Dubarry (Shirley Henderson) canoodling with a man other than her fiancée, lingerie designer Joe (Ciaran Hinds). Avidly seeking stardom, Delysia is eager to be discovered; hoping to avoid disaster, Miss Pettigrew is eager not to be.

And that is the set-up, but that really just provides an arena for McDormand and Adams (and the rest of the supporting cast) to do their stuff. Adams is eager and bright-eyed, like Carole Lombard or another screwball heroine of the film's time; McDormand flips between frantic desperation and struggling to project an image of unperturbed professionalism. Director Nalluri (a veteran of British television) also understands an often-forgotten principle of comedic construction: For one of your actors to give a scene-stealing performance, there has to be a scene of value for them to steal in the first place. When Nick comes home just after Phil has been ushered out, the combined efforts of Miss Pettigrew and Delysia to hoodwink him are perfectly constructed, as they baffle him with white lies and swiftly arrange excuses and explanations behind his back.

Miss Pettigrew Lives for a Day has moments like that, and other moments providing everything you'd like to see in a bright, brassy showbiz '30s farce: Slammed doors and lucky coincidences; whispered imperatives and triple-layered double-talk; the comedy rule of threes; the low behavior of the upper class; the moral wealth of penniless persons; the public revelations of private feelings. And there's much comedy wrung from the distance between Miss Pettigrew and Delysia: Offering Miss Pettigrew an adult beverage for a quick shot of fortification, Miss Pettigrew explains she's never had a drink. Delysia is quick to clarify: "Oh, it's not a drink, really; it's a cocktail." And so, down the hatch.

But Miss Pettigrew Lives for a Day also gets energy and power from being honest about when it is set, and when it was written. Miss Pettigrew walks the line at a soup kitchen for the homeless; newspaper headlines threaten war. And at a cocktail party, as the sky is darkened by bombers and the roar of their engines drowns out the music and laughter, the bright young things in attendance gather on the balcony to cheer. Inside, Miss Pettigrew sits, sad and worried: "They don't remember the last one." "No," Joe commiserates, "they don't."

Moments like that make Miss Pettigrew Lives for a Day much more satisfying; we know what's at stake, and so do the characters. And while Adams' giddy, giggling nymph is good for many laughs, she also gets a few richer, deeper moments, too; McDormand also has moments of broad physical comedy (a very rushed cleanup, for example) that she balances with smaller, subtler moments like the play of emotions on her normally stoic face when she realizes things may, in fact, work out for her. Miss Pettigrew Lives For a Day may be a fairly small-scale comedy, but it delivers tremendous satisfaction, and that's a victory in and of itself not just for those who made the film but for those who'll see it.