In Bjarat Nalluri’s film of Winifred Watson’s 1938 novel, Miss Pettigrew’s “Day” starts out rather pallidly, but it gradually gathers steam to become a pleasant outing for the audience as well as most of the characters. The picture will especially charm women of a certain age, the way the similar “Mrs. Henderson Presents” (2005) did, but if this sort of period fluff appeals to you, whatever your years, it’s a good example of it.

Frances McDormand practically channels Emma Thompson in the title role of Guinevere Pettigrew, a frumpy would-be governess in pre-war London who’s down on her luck after flubbing several jobs. Disowned by her agency, Miss Pettigrew surreptitiously absconds with the address of a potential employer and goes to the plush art deco suite occupied by high-spirited singer Delysia Lafosse (Amy Adams), who’s just finished a night’s stand with Phil (Tom Payne), the handsome young son of a theatrical producer, in the hope of securing the lead in his father’s new show. Pettigrew is shocked at the situation, but saves the day for Delysia when Nick (Mark Strong), the actual owner of the flat (and the demanding proprietor of the club where Delysia sings) shows up expecting Lafosse to be sedately—and compliantly—awaiting his return.

Her quick thinking in this potentially ruinous situation secures Pettigrew the job of Delysia’s social secretary, and before long she’s off to a fashion show with her new boss, where she’s introduced to both gentlemanly Joe (Ciaran Hinds), a lingerie designer, and shrewish boutique hostess Edythe (Shirley Henderson), to whom he’s engaged despite their apparent incompatibility. Guinevere charms him with her utter lack of pretense, but after the couple break up Edythe forces her to aid in getting them back together again by threatening to reveal Pettigrew’s previous shabby existence if she refuses.

But there’s another wrinkle in the plot, in the form of Delysia’s accompanist Michael (Lee Pace), just returned from a brief jail stay, who’s obviously in love with her and wants her to return to America with him. So the young woman is faced with making a choice among possible stardom with Tony, a life of luxury (if also subservience) as rough Nick’s kept woman, or real if penurious romance with handsome Michael.

This being the kind of picture it is, there’s little doubt about who Delysia is going to wind up with, or about the part Miss Pettigrew will play in her decision. Nor is there much uncertainty about the fact that Guinevere herself will find companionship and the promise of future happiness, even as the winds of war begin to blow. What’s important about “Miss Pettigrew Lives for a Day” isn’t so much where it will wind up, but how enjoyably it gets there, and after a first act of what amounts to bedroom farce that comes across as rather stilted and affected (with performances to match), the movie finds a gentler, less frenetic pace that adds a touch of warmth to its initially too brittle feel and becomes quietly charming. The cast benefits from the transformation of tone as well, with McDormand adding layers of shading to her character while Adams gradually sheds the simple artificiality of the early Delysia—the ditzy, overambitious bombshell—to fashion a more likable and rounded character as well. And while Strong and Payne remain essentially one-dimensional (as does Henderson in the thankless part of the manipulative though well-groomed Edythe), the addition of Hinds and Hinds, both of whom make for very sympathetic alternatives, helps immeasurably.

The picture boasts a very attractive appearance, with a fairy-tale period look provided by the production design (Sarah Greenwood), art direction (Niall Moroney and Nick Gottschalk), set decoration (Katie Spencer) and costumes (Michael O’Connor), lovingly captured by John de Borman’s luscious widescreen cinematography. Paul Englishby’s music adds to the atmosphere without calling undue attention to itself, as so many scores do in comedies today.

They all add to the delight of a picture that’s really nothing more than a bright, sugary confection, but one that goes down easily.