Is there any role Frances McDormand can't play? I guess I'd like to see her as the evil genius behind some grossly murderous scheme, something she hasn't yet played as far as I know. But in "Miss Pettigrew Lives For a Day," set in 1939 London, she is the plainest, drabbest, mousiest governess ever, who's been fired from all her jobs, usually by losing track of her charges, until she steals a card from her agency employer for one last chance. In the meantime she has no money, no wardrobe, and hasn't eaten since forever, it seems.

What she finds at her new employer's house is not children but a flighty woman named Delysia LaFosse (Amy Adams), a singer who's currently juggling three boyfriends in hopes of getting the lead in a West End musical. It's she herself who needs the governess, and Miss Pettigrew finds that she is up to the task.

This film is the lightest possible meringue of a fairy tale, so light that at times it's in danger of floating away. The day that Miss Pettigrew spends with Delisia starts with getting one lover out of bed before the second one comes in the door, then goes to a fashion show of underthings at a department store, designed by a middle-aged man named Joe (Ciaran Hinds), who is engaged to one of Delicia's backbiting young friends.

There's a party at Delicia's that afternoon, where we'll meet Michael, her not-so-wealthy accompanist on piano, who really loves her and wants to take her to New York on the Queen Mary, which is leaving the next day. Will she go? Will she stay and be a star in London? Are you even worried? This is a fairy tale, in case you weren't paying attention.

In any case, Miss Pettigrew manages to find it in herself to arrange things quite well, though there is a running gag in the film that every time she takes some food, something keeps her from eating it. And Frances McDormand, the plainest face in the world, manages to shine with an inner light that is wondrous to behold. Amy Adams as Delisia is a little over the top here, putting a little too much into every shrug and mue; she was much better in last year's "Enchantment," where she played a fairy-tale princess. "Miss Pettigrew" isn't a perfect fairy tale, but in a lean spring it'll have to do.