The couple, known only as Mr. and Mrs. X (Laura Linney and Paul Giamatti), ask her to serve as a nanny for their young son, Grayer (Nicholas Resse Art), after Annie saves him from an accident.

Annie, whose real interest is not in finance but in anthropology, thus enters a "culture" quite alien to the working-class world in which her hardworking and affectionate single mother (Donna Murphy) has raised her.

This new world is one in which fathers are callous and philandering, mothers are empty-headed, lazy and self-absorbed, while children like Grayer are, at once, overprivileged and neglected.

As Annie tries to meet Grayer's needs, contend with the endless demands of Mrs. X and keep Mr. X at bay, she must also conceal the reality of her new situation from her mother, whose high-flying career ambitions for her daughter do not include the role of nanny.

Thus, just about the only people Annie can rely on to guide her through the minefield of stress in which she now finds herself are her two closest friends, Lynette (Alicia Keys) and Calvin (Nathan Corddry)

Eventually, she also manages to win the sympathy and affection of one of the Xes' neighbors, a handsome young man from an affluent background (Chris Evans) . Since Mrs. X fired her last nanny for going on a date, however, the blossoming romance between Annie and her new beau is just one more complication.

Torn between her love and concern for Grayer, and her resentment toward his parents, Annie is paralyzed with indecision. Should she stay and look after her young charge, whose parents' marriage is swiftly falling apart, or should she break free?

"The Nanny Diaries," written and directed by Shari Springer Berman and Robert Pulcini, clearly aspires to be a comedy of manners and a keen-eyed expose of Upper East Side decadence. Yet its fundamental message, that the rich are bad and the working class is good, is far too simplistic, while the characters who populate the film are, with a few notable exceptions, little more than stick figures.

Mrs. X does have a sympathetic dimension, since she is vulnerable to her husband's bullying and neglect, and she ultimately proves redeemable, both as a person and as a mother. But the other wealthy characters are uniformly selfish, including Grayer's liquor-swilling grandmother.

Given the shallow characterizations, there are few opportunities for more than competent acting. Johansson convincingly carries almost the entire film on her shoulders. Linney ranges ably between a snobbish shrew and a disappointed little girl. Young Nicholas Reese Art has quite a range himself, and can kick Annie's shins or win her heart with equal skill.

Two other pluses: The film's cinematography is lush, and there are some skillful and amusing special effects.

The film contains one use of the f-word, some crude and crass language, occasional profanity, partially concealed sexual activity, sexual advances, implied adultery and premarital sex, brief gay references, brief female disrobing without nudity, and implied divorce. The USCCB Office for Film & Broadcasting classification is A-III – adults. The Motion Picture Association of America rating is PG-13 – parents strongly cautioned. Some material may be inappropriate for children under 13.

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Mulderig is on the staff of the Office for Film & Broadcasting of the U.S. Conference of Catholic Bishops.